Sorry, but to take that sentence by Voltaire verbatim under all circumstances is silly in my eyes, for we all agree that for instance in that 'fire' situation free speech can be restricted by the law. So we only disagree about from where on restrictions should be put on free speech and not whether at all.

It is a principle and a very good one, if a difficult one to follow. That it may be difficult to follow does not make it any less good as a principle.

So where should restrictions be placed on the freedom of artistic expression?

Simply in all cases where someone risks being upset by it? Or only when you don't like what is being said?