“I think the point is that if it’s their established Minhag, it’s not an aveira.”
I’ve never understood this. In some circles, especially the chassidish world, there is no system of checks and balances when it comes to minhagim. Anything that may have once been can be passed off as a minhag, or mesorah, even if it involves an aveirah or something that’s a distortion of the Torah. Why is this?