if we don’t approach them in a respectful way, how could they ever understand what they are doing is very very harmful?
Who says the goal is to help them understand that they are being harmful? Who says they don’t know? Maybe they do, but don’t care. Even if they don’t know, why assume there’s anything to do about it? They’re not going to listen to us either way.
I think our job is to distance ourselves from them and try to minimize the chillul Hashem as much as possible.