Like someone said before, you can't fight racism and promote it at the same time. If you want to take up the stance that America is racist, so we should start being racist too, I don't agree that, but I'd say it's a fair stance to take. However, the people that feel that way, need to stop bitching every time a white person does something racist. The main people that think something like this is cool are the ones that cry the loudest when white do their foul shit. You can't have it both ways. It's not about standing on moral high ground. It's just the reality of the world. Either you're going to hold yourself to a higher standard and push for others to do the same. Or you're going to embrace the low standard and take everything that comes with it. You're lying to yourself if you think there are any other options.
It depends on how its done. Like I said, I don't know that a music festival is really the place for that, but I do think there are times when blacks should be able to say "Blacks only." For example, if there is a conference where blacks are coming together to try and plan out a political strategy for push black issues (e.g., reparations), the people involved should be able to say "Blacks only." If whites don't like it, then fuck 'em in that case. Blacks aren't beating down the doors to get into white nationalist meetings.