Cultural relativism is definitely something that can be tricky because of the fact that it says to be tolerable of different moral beliefs and actions in cultures but there are some things in certain cultures that are just intolerable and we all know are wrong. Such as things like mass murder, slavery and racism as you mentioned in your post above. We can all see that those things are morally wrong but does that mean that we have to be tolerable of those cultures values? This is where cultural relativism contradicts itself because we know its not morally right to do these things and these acts shouldn't be tolerable in anyway.