This thread isn't going to resolve anything on this "issue"; just look up affirmative action. There's the logic you provide, which is solid. The counterargument is that certain groups currently have a major disadvantage and specifically targeting them improves things, despite it excluding on race or other characteristics. In this case, it may be that "black girls" wouldn't feel comfortable or would be significantly outnumbered in a general "group of humans" so excluding people provides a net benefit in this case.

Another view is that private groups should be able to do whatever they want, and discrimination is only a problem when it's a problem. If "black girls" grew to dominate the industry or significantly change things, then it's become problematic. Obviously that's a rather subjective measurement hence all the "debate".