I don't think I've ever sent a PM because someone offended me.
I have to disagree with the idea that it doesn't matter what someone you don't know thinks. Of course for certain things that's true, but it does have an effect on me, even indirect as it may be, that someone holds racist/sexist/etc. views. Those things affect everyone. Now I get that the odds of changing anyone are slim, but then there are people who will tell you that they did change, and it was because there were people who were willing to question and contest their views.