We literally have seen black people say don't take our words, and only black people can speak like this/say these words, are you saying they were wrong to want that?

Also, cultures mixing doesn't work like this, it isn't taken, but given freely.

Edit: As we said, it harkens back to a long history of colonialism and people taking things that aren't theirs.

Edit 2: Also, no, one culture only being allowed to use a langauge isn't the source of its invalidation it's 'official' forces like school, government etc not recognising it as a langauge, not people saying it shouldn't be appropriated, you're still welcome to learn and understand it, just don't use it. It really is that simple.

Edit 3: Also people online taking it and changing it to fit their own needs, using it to the point parody, not recognising that black people invented it, and saying it's a 'meme' also invalidates it as a language. It's literally a language they needed to create in order to survive, having it memeified is disgusting and misses its entire point.