Ah. Well. This was probably unavoidable. Tanya really hopes this doesn't make Belmarniss mad at her, but she doesn't want to lie to her either.
"On Earth there are many religions, and there were many more in the past. They make entirely contradictory claims - about what gods exist and what they want, about magic and miracles and the afterlives, about the right way to live. Many past wars were religious ones, because some religions call to convert other people by force. And although most of them tell stories of past miracles, none of them are granted verifiable miracles today. In the modern era, improved technology has made people richer and safer, and some religions have lost the political power they once had. Many people now believe that all the religions are false; there's a common joke that religious people believe all the religions are false but one. In any case it is obvious that religious beliefs are not caused by being true, because everyone believes something different and which beliefs are more common mostly depends on which people conquered a place long ago."
"My opinion on religion, which is not unique to me, is that it's a complex social force which can do both great good and great harm. Unavoidably so, because it plays such a large part in people's lives and in society. Many specific religions do much more harm than good. Dogma, claims which can't be proven from observed reality but you're not allowed to contradict, are very harmful to rational thought. Churches, like all organizations, try to grow and gain more power and they don't pay society enough for the privilege, because the way they purport to pay society is by teaching religious law which is false. And they encourage antagonism towards countries with majority populations of other faiths. All the good things they sometimes do, like organizing charity and public works, could be done just as well by secular organizations in a society that had no religion."
"I do know that beings exist that can interfere in the world." For personal reasons which she has no particular reason to hide anymore, but which she'd rather not reveal because they're hard to believe and don't actually contribute anything to the conversation. "They are not to my knowledge the gods of any specific church, but I don't know much about them. The thing about religion is that it's built on falsehoods, even if people honestly believe them, and nothing good can come of that."