To me, it seems that there are people that you know are racist, but that's a smaller and smaller fraction of people as time goes on. When someone adds themselves to the list, then you can be disappointed, sure, especially if they were someone you respected. But you should then go on to deal with people who are not on the list.
And as for "just let him be"... you exposed him on HN, which might matter rather a lot to a VC.