You may also be interested in these two posts I made, the first on quranic errors, the second on the historical evidence of Moses, the prophet most mentioned in the quran.
So I thought I'd expand on the above, because I honestly meant these to be arguments.
1) The quran:
The quran claims itself to be the perfect uncorrupted word of god. That's it's biggest flaw. It invites challenge in a way other holy texts don't, and is really to arrogant for it's own good. The level is enough that it doesn't have the flexibility needed to stand the test of time. The fact that it doesn't have this flexibility, and that it needs it in the first place, is an argument against it in my opinion.
2) Sanity
There's only so much a human being can reasonably be held accountable for when it comes to spiritual matters. There's a verse in the quran which says allah has not given us two hearts. I personally view this as metaphorical, not literal. We view and believe certain things a certain way. I cannot at the same time believe in the quran while seeing flaws in it.
3) Reality
The quran, like all the other holy texts, claims to be the word of god. The way to verify this is testing it, see if it stacks up. Quite frankly it doesn't. Dust devils and jinns, spontaneous human creation, great flood, there's a lot to choose from, but I'll pick a few.
The story of the arc and the great flood. This would have happened around 4000 years ago. It's quite simply impossible for the number of races, ethnicities and the huge amount of genetic traits to come from one incestuous family in just 4000 years. It cannot happen. Something else that puts a hole in the story is the amount of people who were thriving at this point. God flooded the entire world. Except for the Chinese who were developing at an incredible rate and remained unaffected from a global flood that wiped out every human on the planet. The Japanese were also unaffected. And the Africans. And the Europeans. And the Native Americans. And the Aztecs. And the South Americans. And most of the middle east. The flood never happened. It's not real.
The quran teaches that humans were created from clay in a specific creation. If you're to count on the hadiths, then it's just even more ludicrous. We know the first human was not a 90 foot tall clay giant. Even if you don't take the hadiths into account, it also doesn't account for evolution, the proof of which is overwhelming. Nor does it account for the number of people today who have Neanderthal DNA in them from before the Neanderthals went extinct. Everything I know to be proven fact contradicts the claims of the quran. The only logical conclusion I can come to is that it was a story told by ancient societies because they didn't have any answers. Adam never existed. It's not real.
The sun orbits the Earth...yeah, we've known that's bullshit for a few centuries now.
It says in the quran that in the embryo/foetus the bones are the first thing to form. "So we made the clot a morsel, so we made the morsel bones, so we clothed the bones (with) meat". This is wrong. The skeleton is actually among the last to be formed. You'd think the all knowing creator of everything would realise this. It's wrong.
The stars are missiles to be hurled at jinns. Or they hunt demons. I haven't read the quran in a while so I can't remember the exact quote, but you can look it up to see exactly what it says. This is also wrong. The stars are just stars, they do the exact same thing as the star we orbit, the sun.
Women are defective in intelligence. Coming from a culture where gender mixing is the norm and close relationships aren't looked down upon, I can tell you this isn't true from my own experience. And then there's current trends in school grades, sciences, IQ and employment performance, the fact there are women in MENSA (if you don't know MENSA is like a super genius club, only 2% of the human population globally have a high enough IQ to qualify for membership). Now we live in an age men and women have equal rights, women are on the same level and even starting to out preform men. So I'm going to say this is wrong.
4) Nonsense
Do you believe that allah puts a veil over our hearts? If the answer to this is yes, then my reply to that would be that I'm blameless. If the reason I don't see the truth of islam is because allah put a veil over my heart, then it stands to reason I'll be punished (by being sent to hell) for a crime I didn't commit. My reason for saying I'm being punished for a crime I didn't commit is that allah delibertly put a veil over my heart so I would never know him, therefore the fault is allah's, not mine.
Do you believe nothing happens accept by allah's will? If so then it's the same as above. If nothing happens except by allah's will, then allah made sure I wouldn't believe in him. So again the fault lies with allah, not myself.
Do you believe islam teaches there's no compulsion in religion? If so does that mean if you don't accept islam as true, then you go to hell? If so, this means that allah has told us something to be taken as truth, and he punishes us for taking him at his word instead of assuming he was lying.
Do you believe in the virgin birth? If so, can you understand why I might think it's more likely that a teenage girl told a lie rather than a virgin magically conceiving a child, carrying it to term, birthing it, and the child while still an infant speaking?
Can you also understand why it may be confusing that said infant would only speak once to a few people and refuse to speak again to others, which would cause all doubt in the divinity of allah to be wiped away?
Here's a situation. Let's say there's something in your house you don't like. It offends you. Let's also say you have the power of a god. Would you A) throw away the thing you didn't like or give it to charity, or B) bring it to life, give it intelligence so it can understand what's happening, enable it to feel pain, and torture it forever and ever and ever? Which is more merciful?
5) Common sense
It becomes a common sense issue. Let's say that I'm wrong. Let's say all the things I'm of the opinion are true are wrong. It doesn't change the fact that I find the quran unbelievable. I can't have more knowledge than what's available to me. Let's take evolution. I find it believable. I'm convinced of it. The quran goes against it. I have no reason whatsoever, nothing at all compelling me to believe the quranic story over proven scientific fact.
Or another, let's take the big bang. I'm convinced by what knowledge I have that before the universe, and after the universe, there was no Earth. This planet did not exist. It took a very long time for our star to be born and for our planet to form. This seems plausible to me. From what I know of physics and cosmology, I can accept this. I have no reason whatsoever to believe that the Earth existed from the start and was ripped apart from heaven.
Or another. The quran and hadiths suggest a flat Earth. At one point it's spread out like a carpet, at another the Earth is like an ostrich egg (had to pick the bird that buries it's egg and flattens the soil), allah will roll up the Earth like parchment/paper, and on and on it goes. Everything I'm aware of tells me this is wrong. It becomes less and less believable to me. So with all this in mind, common sense tells me that the only truth that lies hidden in the quran is simply the truths of the cultural norms and mindset of that society and time. Historically and psychologically it's interesting, but that's all it is. No more, no less.
And I have to admit, these aren't even my strongest arguments. I haven't thought about this endlessly, I haven't delved into the theology to throw things at you. The above is just what came to mind as I sit here filling the time on a lazy Sunday evening.
There's no evidence at all, for any of it. Not for a historical Moses, not for the slaves, not for the plagues, not for the desert wanderings, nothing. I'm a little drunk right now but I'll try to give an idea.
The first thing to mention is that there's no real evidence of jewish slaves in ancient Egypt, at least not in the scale the abrahamic religions would have us believe. At the time of the supposed uprising there were 600,000 families, which works out to about two million people. Two million people who lived under hardship and tyrannical rule. Let's not even mention that the ancient Egyptians treated slaves as a common practise in ways that are completely contradictory to this. Let's not even mention that they couldn't of built the pyramids because they were supposedly enslaved around three centuries AFTER the completion of the pyramids in 1750 B.C.
First off, the Egyptians kept good records. It's how we know so much about them. If they lost two million of their slaves, the economy would have collapsed overnight. Never happened. The competing empires would have smelled blood in the water. Never happened. There's not a single footnote even among the Roman Empire that says "Hey, hear what happened in Egypt?" It would of been big news. No mention of it. Anywhere. Nothing.
The desert they were lost in for 40 years? 120 miles across. They could of walked from one end to the other in a week. There are people who crossed the width of America, which is what, 2700 miles? 3000 miles? Took them a year. The better part of three thousand miles and you cross it in a year. 120? Two million people, used to the desert, are lost for four decades.
You also have to wonder why they did it in the first place. Egypt is basically the Nile. Just 50 miles the other way a huge body of fresh water that no one knew was there. If god wanted them safe, wouldn't that make more sense? But no. Two million desert natives lost for 40 years in a desert they would of crossed in one week.
While living there for all that time, they left nothing. No pottery. No hebrew writing. No camp remains. No food remains. No place of worship, no discarded or ripped piece of cloth, nothing.
And that really sums it up, there's nothing. No records of losing a quarter of the entire population. No records of economic downturn. No evidence of families surviving in the desert. There wasn't even a labour shortage.
You'd almost think it was made up.
The entire story seems to be a plagiarism of Sargon of Akkad, a story that pre-dates Moses by a millennia. While he was clearly a brilliant military leader, it was the story he told of his youth and rise to power that exerted a powerful influence over the Sumerians he sought to conquer. Instead of representing himself as a man chosen by the gods to rule, he presented a much humbler image of himself as an orphan set adrift in life who was taken in by a kind gardener and granted the love of the goddess Inanna. His mother could not reveal her pregnancy or keep the child, and so she placed him in a basket which she then let go on the Euphrates River. She had sealed the basket with tar, and the water carried him safely to where he was later found by a man named Akki who was a gardener for Ur-Zababa, the king of the Sumerian city of Kish. In creating this legend, Sargon carefully distanced himself from the kings of the past (who claimed divine right) and aligned himself with the common people of the region rather than the ruling elite. Sound familiar?
Just to give a clear idea, compare his birth to Mose' birth in the bible and quran..
Exodus 2, 1-10
And there went a man of the house of Levi, and took to wife a daughter of Levi.
And the woman conceived, and bare a son: and when she saw him that he was a goodly child, she hid him three months.
And when she could not longer hide him, she took for him an ark of bulrushes, and daubed it with slime and with pitch, and put the child therein; and she laid it in the reeds by the river's brink.
And his sister stood afar off, to wit what would be done to him.
And the daughter of Pharaoh came down to wash herself at the river; and her maidens walked along by the river's side; and when she saw the ark among the reeds, she sent her maid to fetch it.
And when she had opened it, she saw the child: and, behold, the babe wept. And she had compassion on him, and said, This is one of the Hebrews' children.
Then said his sister to Pharaoh's daughter, Shall I go and call to thee a nurse of the Hebrew women, that she may nurse the child for thee?
And Pharaoh's daughter said to her, Go. And the maid went and called the child's mother.
And Pharaoh's daughter said unto her, Take this child away, and nurse it for me, and I will give thee thy wages. And the women took the child, and nursed it.
And the child grew, and she brought him unto Pharaoh's daughter, and he became her son. And she called his name Moses: and she said, Because I drew him out of the water.
Surat Al-Qaşaş 2-13
These are revelations of the Scripture that maketh plain.
We narrate unto thee (somewhat) of the story of Moses and Pharaoh with truth, for folk who believe.
Lo! Pharaoh exalted himself in the earth and made its people castes. A tribe among them he oppressed, killing their sons and sparing their women. Lo! he was of those who work corruption.
And We desired to show favour unto those who were oppressed in the earth, and to make them examples and to make them the inheritors,
And to establish them in the earth, and to show Pharaoh and Haman and their hosts that which they feared from them.
And We inspired the mother of Moses, saying: Suckle him and, when thou fearest for him, then cast him into the river and fear not nor grieve. Lo! We shall bring him back unto thee and shall make him (one) of Our messengers.
And the family of Pharaoh took him up, that he might become for them an enemy and a sorrow, Lo! Pharaoh and Haman and their hosts were ever sinning.
And the wife of Pharaoh said: (He will be) a consolation for me and for thee. Kill him not. Peradventure he may be of use to us, or we may choose him for a son. And they perceived not.
And the heart of the mother of Moses became void, and she would have betrayed him if We had not fortified her heart, that she might be of the believers.
And she said unto his sister: Trace him. So she observed him from afar, and they perceived not.
And We had before forbidden foster-mothers for him, so she said: Shall I show you a household who will rear him for you and take care of him?
So We restored him to his mother that she might be comforted and not grieve, and that she might know that the promise of Allah is true. But most of them know not.
Sargon -
Sargon, the mighty king, King of Agade, am I. My mother was a vestal, my father I knew not, while my father's brother dwelt in the mountains. In my city Azuripani, which is situated on the bank of the Euphrates, my mother, the vestal, bore me. In a hidden place she brought me forth. She laid me in a vessel made of reeds, closed my door with pitch, and dropped me down into the river, which did not drown me. The river carried me to Akki, the water carrier. Akki the water carrier lifted me up in the kindness of his heart, Akki the water carrier raised me as his own son, Akki the water carrier made of me his gardener. In my work as a gardener I was beloved by Ishtar, I became the king, and for forty-five years I held kingly sway.