I have a hard time believing there aren't plenty minorities out there who would get these tattoos that don't hate other races. I believe Cain doesn't, but that's just a judgment I've rendered from his persona. The possibility of being wrong is there however. This isn't apples and oranges, because you know you are getting an apple when you bite into an apple, and you know you are getting an orange when you eat an orange. You don't know what kind of person you are getting with a "[Whatever race] Pride" tattoo. I refuse to sweepingly generalize anybody as either "pride[ful] in own ethnic background" or as a white supremacy lover. There shouldn't be a factor added to decide if something is a double standard or not.. in this case it would be a historical factor. But there could be some other factor (like a statistical one, or others). That's why the double standard exists in the first place.
I looked up Dunbars number and I'm not really sure how you'd want me to apply it here, but I'm not trying to judge every person on the planet as an individual because I can't know every person on the planet. Everybody will know a select number of people throughout there life and they should just judge those select few as an individuals, not judging before they even know them by some preconceived notions. If I met one person with "White Pride" and one person with "Black Pride" (2people<Dunbars 150), then I would get to know what they are about before assigning one assumption that's equitable for their motivation behind having it and the other with an inequitable assumption in contrast to what I gave the other.