I think that ridiculing and satirizing politicians, terrorists, big business, failling public services etc is fine - they are fair game. Private Eye does this very well. I do however, even as an agnostic, think that ridiculing others' religious beliefs is not so acceptable because it strikes at the heart of who people are. I think it is right to lampoon Islamic terrorists, but not the religion itself, which is in fact peaceable.
Paradoxically I think people should have the right to do so, but hope that they have sufficient sense of respect for others' feelings not to seek to offend to no purpose, and with no particular point to make.
Once again I have to say that I in no way defend these barbarisms. Journalists need to have the right to be tasteless without getting murdered.