And it's a close cousin of "it's all good", which is one of the most idiotic sayings I've ever heard.

If it's all the same then there is no basis for a value judgement and it can't be "good". Entirely appropriate that it came from rap culture.

Maybe it was meant to be ironic, like the use of the N-word in rap music. If so, it has taken on a life of its own. The audience didn't get the joke.