So my question is, should there be discussions about religion in English class or not?
Yes, discussions about religion are possible in English class but it usually requires great tact
. It's not something you should avoid at all costs, but I recommend not "defending" (saying you support) a particular idea or point of view. It's best to allow your students to express their opinions without you actually saying what you think about them. They are the ones who need practice with the language, not you. Your opinions must be as neutral as possible so as not to cause any controversy.
Try to create a relaxed atmosphere - listen non-judgmentally (and listen more than you speak). That way, things will always turn out fine.