Many religions are a packaged deals. Meaning they have their own metaphysical beliefs, morality, commandments etc. If people only take some parts of it and not the other, then there will be injustices not only by the outsider’s morality but also the insider ones.

Anyways, today we have laws that have largely replaced religion’s morality and social justice elements precisely because mixing and matching multiple different moralities and justice systems wasn’t very good. So i guess its fine to mix beliefs today