An interesting analysis of taking the piss out of religion is to be found in the Sunday Times (UK).
The thesis, indeed the headline, No religion should be above criticism, is that religion belongs to us all, and no one has the right to tell us to respect it, to disrespect it, not to make pieces of art about it, not to depict it in movies and so on and so forth.
That goes for all religions, of course. But one thing the writer talks about is an exhibition in which visitors were urged to write things in a bible. Imagine getting away with that if it were the Koran!