But Islam DOES NOT mean "peace". Islam means submission to God. Personally, I think all men have to submit before the awesome majesty of God sooner or later. I'm not particluarly ritualistic ir religious, but when you look at creation, you realize that you are small and pathetic before God. In the face of that, submission is quite realistic.
Way I see it, God gave us life-- and in His mercy-- gave us hope. That's enough for me. I submit.
As far as what you've read about Mohammed-- most of it is wrong. Mohammmed never ordered men killed. He killed them in combat (kind of like Solomon and David) or he passed judgement on men who violated the law.
As far as marrying a 6-year old-- that's simply not true. Mohammed married Ayesha at 17. If you read the Old Testament or the Talmud, you'll find that the Hebrew prophets married early and often. And frankly speaking, in that century (7th), Euros and Middle-Easterners all married young. Indeed, the idea of consent age is a rather recent one.
Note this, though. As angry as I might be at assualts on Mohammed by Christians, I ( and even the most twisted Bin Ladenite Muslim) would never assault Christ. It would be easy. But it would be unthinkable. For Christ is sacred to us, and an assault on Christ is an assualt against the faith of the one God.