What if someone wasn't actually an official member of the KKK and they didn't donate or anything, but they still believed in that ideology? Personally, I just wouldn't hang around with anyone like that, but if I found myself unable to avoid their company... well, I don't know how I would react, but how I think I should react is to let them know exactly what I think of them.
I agree that political discourse would benefit greatly from a bipartisan mass-intake of chill pills, but at the same time, if, after suspending judgement and engaging politely with a person they reveal themselves to be selfish and uncaring, I would stop respecting them privately in my own head, and I don't see anything wrong with making it public. In fact, I would argue that anything less contributes to the normalization of whatever terrible beliefs they hold.