I’d say the same thing that I’d say to someone who really likes Swastikas but doesn’t want to be affiliated with Nazis. Too bad things worked out this way, but people have to weigh their priorities. Just realize that if you don’t want to be read by others as racist, you shouldn’t wear blackface. If a person decides their halloween costume looking a certain way is more important than whether other people think they are racist, they can deal with the fact that people think they are racist.
Maybe this isn’t cross-cultural and universal, but it’s definitely true in North America.
