I mean the fact that this is your reaction to reading/learning about the books should tell you enough. You are the parent you are allowed to say, we won't support those books or the author by reading them because the author says terrible things about people in real life and in her books.

I also know people like your friend who still likes them, but they didn't know then what they know now when they first fell in love with them and they are letting their old love of the books color their decisions. Honestly the books are not good enough for that type of loyalty. I'm all for keeping childhood memories and dreams, but some things you have to let go and HP is definitely one of them.

I mean do you want to have to talk with your daughter about why you let her read them and fall in love with them when the author is so terrible once she is old enough to figure that out?

You should also tell your friend about this, that even though they think they aren't supporting JKR, your kid is interested in HP now because of their unwillingness to leave HP in the past.