That's because you are a far more lenient person than I. "You should know what you did" argument is for 1950s housewives. If I'm spending time around someone, I'm working on the assumption that they aren't out to hurt me, so if they do, I'm going to guess it's by mistake, and they aren't aware of it.

I don't think as a black person it's my job to educate white people about racism. But if they are part of my circle either they are worth my time, or they shouldn't be part of my circle anymore.