Try to look at religion from outside it. If you look at the beliefs and superstitions of people over the last millennia, you'll realise that God has always been around, in many different forms (Weather gods, volcano gods, creation gods creating life out of ooze, water, trees, ... depending on which culture in which part of the world is preaching it). Allah is just one form, that was created after a sequence of other gods before him.
Muhammad was not a prophet. He was simply a 7th century man who lived in a time where much was unknown and the invocation of a supernatural being was almost necessary to not lose your mind on how the world works.
"But Muhammad did have good teachings"
Agreed, but he also had bad teachings. The good teachings are those that we today regard as basic morality (respect, mercy, ... although he didn't always comply to those very rules). The bad teachings are those that were compatible with his day and age, but incompatible with ours (slavery, extreme punishments [sharia], oppression of women [half inheritance, coverage, beating them but not vice versa]).
So again, this makes more sense if we regard Muhammad as a 7th century man, claiming to hear God, rather than regarding him as a prophet of God delivering a final, ultimate message.
Al-Hallaaj was one of the most well known heretics who were put to death without being asked to repent. Al-Qaadi ‘Iyaad said:
The Maaliki fuqaha’ of Baghdad at the time of al-Muqtadir were unanimously agreed that al-Hallaaj should be killed and crucified because of his claim to divinity and his belief in incarnation, and his saying “I am al-Haqq [God],” even though he outwardly appeared to adhere to sharee’ah, and they did not accept his repentance.
In ancient cultures they used to sacrifice animals. Later cultures, influenced by the local religion, moved on to sacrificing humans, in the name of their God. Same bullshit, different time/packaging.
Here's a 2-part (objective and reliable, sources are available on Klingschor's blog) biography of Muhammad made by a member of this board.
Watch it and ask yourself: does this profile describe a final prophet, or simply a typical 7th century Arab, with a whole bunch of leadership, trying to save his ass out of the trouble he got in by revealing convenient verses?
http://www.youtube.com/watch?v=8tj1j8089LMhttp://www.youtube.com/watch?v=1DagUWed95E