Two words: FUCK YOU.
Non-Muslims are incapable of committing blasphemy against a religious figure they do not consider divine. You cannot be guilty of a sin that you do not believe exists. Pentacostals believe it is indecent to show the knees and thighs in public. Does that mean my wife is going to hell because she wears a bathing suit at the beach? Of course not. She's not Pentacostal.
A liberal society (in the classical sense) requires that individuals are free to believe and practice what they choose. Someone cannot force me to believe or worship something in which I have no interest. So while it is perfectly acceptable for Muslims to be upset that their "prophet" is depicted in an unflattering manner, it is absolutely unacceptable for them to infringe on my right to create or distribute such a depiction.
But that gets to the heart of the matter, doesn't it? Radical Muslims do not want to live in a liberal society where everyone is free to think and do what they choose. They want to live in a world governed by sharia as interpreted by the most oppressive theology possible. In their riots and protests, these zealots are holding signs that say "KILL THOSE WHO INSULT INSLAM". Well, I say kill those who can't take a fucking joke. The world is not required to live by your 7th Century dogma. The more you kill in the name of your religion, the more images like this will continue to apply: