No, those threats were credible - and clearly must be reacted to in the right manner.
But this protest is reacting to the wider majority of empty threats.
The rest of your post is just worrying. You may not understand why offense is taken at a picture, I agree and to me it seems silly.
But that doesn't give us the right to essentially say "shush, you're being silly. Let us get on with our protest please". It's a bit patronizing :-)
think of it this way: all Muslims are discluded from this protest. How is that unity?
(also, this ain't freedom of artistic expression. It's a deliberate attempt to get at the terrorists with imaea they don't like... That's a negative image in my mind :-))
These threats are highly credible.
I'm sorry if many muslims are offended by this, but that's really to do with their own lack of self confidence. Nobody's lost an eye, limb or a life by the actions of Mohammed drawers. It's a picture, for goodness sake!
Perhaps we disagree about what a positive symbol is. I happen to believe the artistic result of freedom of expression is a positive symbol.