Because when you say something like
It pretty much sounds like the rambling of a white supremacist.
First, it makes no fucking sense. The number of white people isn't changing due to diversity. Diversity isn't causing more non-whites to materialize out of thin air or for white people to disappear. It's just stupid to say.
Second, who the hell cares if there are fewer white people? Why is it any worse than having fewer black people, brown people, etc.? You are racist and implying that white people are more important. You can go fuck yourself.