1. Muhammad was a warlord. This almost singlehandedly disqualifies him. I would expect a person of god to be the peaceful type.
2. His rules are severly degrading to women, such as the law where in court a womans word is worth half that of a man.
3. Muhammad was a pedophile, marrying and having sex with a child.
4. Islam states that half of humanity is going to hell. This is a ridiculous idea, being inherited from a twisted Christianity. No sober-minded person could ever accept such a pathetic, wicked idea as true.
5. The bible is believed to be valid. The bible itself is a completely absurd set of documents which are clearly man-made, just like the Koran.
6. The revelations which Muhammad supposedly received, and that he is supposedly the last prophet, fall short of what one would expect as the last message to humanity. Where is information about genetics? Or about the big bang? Or evolution?
7. A God that is obsessed with worship is another ridiculous idea. Why would anyone want to be worshipped at all, let alone as much as the Abrahamic God demands.
8. How could we think that an all-powerful god would communicate with humans through individuals like Muhammad? God would know that sober-minded people couldn't possibly accept the testimony of, say, Buddha, over the testimony of countless other 'prophets'? If God existed, he wouldn't make such an obvious, foolish error. He would make sure that his message was clear and accepted as valid by everyone.
9. In Islam, people can have up to 4 wives. Muhammad had a lot more than this, another indication that he was in it for power, wealth and luxury, deceiving the masses with lies.
Just another religion, nothing special to talk about. However, the damage that Islam has done to humanity and continues to do is extreme. It will be a good day when no one believes this nonsense anymore, and the religion fades into mythology to join the countless other religions which people don't believe in anymore.