Are you saying that if I believe in monotheism but I believe all the prophets are frauds, then I am still a Muslim?
Good question.
No, because you have to believe in the whole message in it's entirety, which was conveyed by the Prophets/Messengers.
To disbelieve in one, in essence means to disbelieve in all.
The Quran says:
"The messenger believeth in that which hath been revealed unto him from his Lord
and (so do) believers. Each one believeth in Allah and His angels and
His scriptures and His messengers - We
make no distinction between any of His messengers" 2:285
Your question is a good one though, because you're saying if Islam is about believing in One God, why can't one merely just do that, without having to accept the Messengers/Prophets.
Islam means submission to God. So one would have to submit to ALL of what was conveyed in it's entirety to be regarded as a Muslim.
Also can you explain why a human by default might not believe God is an infinite set of spirits - some good, others bad? Or polytheism, which by all accounts of recorded history, appears to be one of the oldest religion on record?
Another good question. I said that God instills in a human being the knowledge of his Oneness. Not that the default position has to be, to believe in one God, as your surroundings and environment will have a far greater impact on you.
For example ancient people used to worship things that inspired their fears, and were thus enslaved by fear. Their deities were based on powers of nature, the moon, stars, win, rain, lightening etc.
Some began to see their ancestors in dreams and proceeded to worship their ancestors. However they wanted something more tangible so they imagined that the spirit of their ancestors had been reincarnated into animals, this is called totemism.
However they still wanted something to take home to worship, so they made idols which represented their ancestors.
Some started to worship rulers and tyrants who exploited priests to their agenda, so they could claim that they were gods or sons of gods, like the pharaohs.
Eventually man progressed and started to cut down the number of gods.
They even (like you said) claimed that there were two gods, one of good and one of evil, one of light and one of darkness.
For example vishnu in hinduism is regarded as the preserver and shiva as the destroyer.
Then there was Akhenaten who brought monotheism to the egyptians, but it was a faulty one because he introduced himself as the son of god. So not pure monotheism.
Whilst all of these man made religions were coming and going, there were interesting developments in other places of the world.
There was a tribe in Kenya called the Kikuyu and they had strong hints of monotheism. They believed in One God called Mogai, who they descibed as Sublime, Generous, Omnipotent, resides in Heaven, Unseen, Creator, Bestower etc.
However they mixed their monotheism by worshipping idols, ancestors, and nature on the side.
In Sudan there was a tribe called shilluk who worshipped One God called "Juok" who they claimed made man from clay, and used various different colours of clay from different continents to make people of different ethnicity.
They claimed he was unseen and invoked him saying "protect us for heaven and earth are yours".
But they claim that he can never make decisions without the permission of Nyikang, (who was their king) and therefore associated partners.
My point is that, there were religions that were completely manmade, and based on their environments and surroundings, and there were other religions that believed in a single God, but then they gave it a cultural and environmental colouring, transforming it into something different.
Messengers/Prophets are meant to bring people back to God and to purify their teachings from what their environments and surroundings corrupted it into being.
Topic: "Revert" or "convert"?