Racism in Harry Potter? Pft. There's not enough of it. 

well, not so much difference with reality. don't you think so?
besides, it's not exactly the main problem of the book. Jo's interpretation of magical world leave a lot of gaps that can be filled by readers imagination. which I think better rather than spelling it/exposing every molecule details. it will make the book dragged on for far too long and leave it with no point/plot whatsoever.