You're arguing on beliefs, on behalf of some Christian interpretations of Islam, and yes, some of them say Islam's based on false pretenses. Muhammed is a false prophet, according to some, and he is found in the eight circle of hell by Dante, etc, etc, etc.
What makes you think that these mainly Christian views (some are Jewish, though, as I recall it) are more correct than the Islam ones?
Here's an argument made by an Imam in reply to a Catholic who doesn't believe in Muhammed as a prophet. I'm not saying that the Imam is right, only that he uses an other set of beliefs than you use, for proving his point.
That's what religions are about, see. Beliefs. You choose to accept some and reject others. Your call. But don't assume that anyone will hail your opinions as informed, when you also use the kind of rhetorics that are usually found on extremist websites. For as long as you do so, I, for one, have great difficulty in taking you seriously.
Only by understanding why some Muslims react so strongly against depicting their Prophet on cartoons or teddy bears can you ever hope to change anything. And I'm not saying that I agree with them, because I don't. Arresting a middle-aged schoolteacher who happened to name a teddy bear Muhammed is ridiculous but insulting the part of the Muslim population (by insulting their religion; this you also need to understand) will not help. Quite the opposite.