For me the line is one of something which is intended to provoke or incite violence/illegal actions. There is no freedom to not be offended. The point on to what extent I can tolerate some political viewpoints/ideologies does make me a little hypocritical as I have a great deal of sympathy for eg the post-war German laws.
That's where I'm at, and I think 'clear intent' has an important role to play... but of course, the objective clarity of a writer/artist's intent is always open to question, especially when it comes to sophisticated and subtle uses of irony in making your statemtent. It almost feels like a cop-out to try to reduce the possibility of misinterpretation, misreading of tone, by telegraphing what you're doing in a foolproof way that anyone can understand, but you can see why many will attempt to subtract some of the sublety from their original draft of a satirical piece when it goes to press.
A good example is the swastika - in some places, you do not have permission to reproduce that symbol in your work, because its historical connotations have made it a 'bad' image. But the swastika can be used to ridicule nazism and fascism/intolerance in general, it can be used to graphically illustrate just how despicable the nazis were/are, and it is a very significant symbol in our dark past, it is a historical artifact of sorts. The reasons for banning its use in media are understandable, admirable even, but are they also misguided?
It's a tricky one, same with the use of racist stereotypes to make your anti-racist point, because these images hold great power to offend and evoke fear and disgust in certain sections of our multicultural society... but is that really a good enough reason to remove them, to make art more "palatable", with no attention paid to the context and the creator's intent?