Very good first thread, and an intriguing question. I'm not familiar with gangsta rap, hip-hop or any of the other genres who seem to be more predisposed towards using racism or sexism in their lyrics, but I would just offer that it's not a new thing (as you point out): bands have been doing it for years --- which doesn't necessarily make it right --- and rock and metal would be another big culprit. I mean, not too many prog rock songs refer to "Girls with big tits" or whatever, unless you extend sexism to speciesism, in which case those guys REALLY have it in for dragons!
Gotta think about this more, will post again. I'm sure there'll be plenty of conflicting replies.
Well done: exactly what we need in a thread: intelligent, well thought-out, bound to create debate and interesting.
And not, to my knowledge, done here before...