Defamation of religion is the idea that one may be guilty of some kind of crime or wrongdoing by speaking insultingly of the religions of others. There have been various efforts to have the United Nations enact some sort of declaration condemning insults against religion on this basis, but those efforts have lost support amidst the growing conviction that the nations pressing them would use such a declaration to oppress their own religious minorities in the name of 'defending' the majority religion from such attacks.
One absurdity which rises above all others within the concept of defamation of religion is the contrary existence of theological exclusivity. Every religion claiming to be the "one true religion" (which is most all of them) inherently proclaims the the invalidity of all other religions. Simply put, almost every religion "defames" every other religion by calling all the others lies. Though I don't wholly buy bull, were I to stand in the street and decry the Bible as a bunch of malarkey, I'd be "defaming" the book, and essentially defaming those who follow it by denoting them malarkey-followers. But this is precisely what the Qur'an does, expressly calling out JC-Bible stories as lies; and similarly the Bible defames Hinduism and Buddhism and Jainism and Pandeism, and the New Testament defames Judaism by labeling as obstinate sinners those who don't accept the whole of its story, and regular old Christianity and Mormonism defame one another, the one by claiming its Scripture can not be added to, the other by claiming an addition to that Scripture which must be taken as true.
So, then, let us get to the bottom line. If we are to be serious about preventing the "defamation of religion," we ought to begin by banning any theology which calls into question the validity of the doctrine of any other theology. And once we were to do so, we'd be left with.... what? Buddhism, possibly, Unitarian Universalism, and some extremely liberal and open-ended variations of Pandeism or Pantheism.