Having read Mishap's description of the cartoons, I too find them crass, juvenile and unnecessarily insulting and whilst I think any religion, ideology etc. should not be deemed a sacred cow and therefore not be beyond criticism, I find these cartoons unbelievably disrespectful. Personally, I'm not happy that anyone's beliefs should be ridiculed in THIS way, I don't think it helps already strained relations.
Apropos of that I have been pondering on other people who have gone too far, for example Frankie Boyle's sexual slur regarding Katie Price's disabled child, or this other bloke Dapper something or other, who I have read about he has a show and has mooted the idea that women are actually gagging for rape. A pretty disgusting assumption I'd say. What is too far? I can't remember the outcome of the Frankie Boyle remarks, I think his show was pulled, I hope it was.
Taking libel out of the equation, is it as Voltaire allegedly said, "I hate what you say, but I defend you right to say it"