There is simply way too much missing info to consider whether criticizing a religion itself would be a viable topic for an exam. It sounds like arguing against Evolution in a Biology exam. I can see arguing against the application of anti-Qu'ranic (word?) behavior while using the Qu'ran to defend it, but just to criticize a specific religion... I'm not seeing how well that carries in an Exam. Heck, the closest I ever came to such a thing was in an essay about Toni Morrison's Solomon's Song... but that was an aside at the end of the essay. I had to demonstrate I understood (read) the book.
It's the exact opposite of arguing against Evolution in a Biology exam, b/c there is no evidence or rational argument against Evolution. So, while students should in fact be encouraged to think critically about Evolution, any essay arguing against Evolution would inherently be poorly reasoned. Critical thinking should be encouraged in every subject, so there should never be disqualification for it, only a failing score if it is poorly reasoned. The only reason people would want a rule that disqualifies such essays is b/c they know the arguments against it could be well reasoned and thus have no grounds to fail an essay that offends people who are committed to falsehoods.
Evolution is presented to students b/c it's objective validity and accuracy makes it highly relevant to many aspect of life. Religions relevance is not that it's valid and accurate, but that people believe that it is. Thus, one cannot actually understand a religion and it's relevance without also understanding how it conflicts with other ideas in society both in science and ethics/philosophy. That is inherently going to make religions look "bad" so long as being in conflict with reason, evidence, and empathy-based ethics is seen as "bad".
"Taking a critical stance" is widely accepted as something that should be more actively encouraged in education of all topics. There is no benefit, and potentially much harm, in simply demanding that students unquestioningly learn what these religions claim without engaging in critical analysis of it. Even treating the texts of fictional literature (which you can guarantee these courses do not), there are valid literary grounds for critical analyses that most adherents of those faiths would fine "offensive". But since the major religions treat those texts as largely factual and historical, then any legit religious studies course should encourage students to critically evaluate their validity as sources of factual and historical information, which than would bring into play not only non-religious historical information but information from the social and natural sciences as well.