The American Muslim, an online newsletter, has issued a statement titled "A Defense of Free Speech by American and Canadian Muslims" that condemns the threats made to Molly Norris (who drew a cartoon advocating Everybody Draw Mohammed Day), and Matt Stone and Trey Parker, the creators of South Park, which included a scene in which the Prophet Mohammed was depicted wearing a bear suit.
The statement says, in part:
Over 80 people have signed the statement; they include leaders of Islamic organizations, scholars, journalists, activists, even a stand-up comic.
Addendum: I wish I had found G. Willow Wilson's response to the incident earlier, as she says it much better than I did:
But the only explanation I have is too simple to satisfy anyone: they happen because hate sells. It sells in the West, where anti-Muslim hate groups feed on incidents of Muslim rage; it sells in the Muslim world, where extremists are only too happy to use examples of Western intolerance to win over new recruits. This is the reality we live in: any satirized depiction of the Prophet Muhammad feeds into a global propaganda war, whether the artist intends it or not. There is no longer any such thing as artistic immunity in the battle of images, and to think otherwise is fatally naive.
And, as she points out, the extremists on both sides get what they want, while the innocent take the hits.