Obviously not all rappers are white, but rap still comes off as a very "black" thing. There have been white rappers since the beginning, when people were rapping over the instrumental breaks in party records, and words have been set to rhythm for much, much longer. Eminem got popular by being good at rapping, and by filling a niche, though he has outlived the novelty of "white rapper". Rapping shouldn't be about race, though. It should be about conveying your ideas through words and rhythm. It has as much variety as rock or electronica, or any other genres. But like other genres, it's easy to get lost in the top layer, the ones that are easily seen on TV and on the radio, and never look beneath. Not everyone WANTS to look beneath, it's fine being comfortable with what you like. I like looking beyond that, finding layers, interesting new tidbits to enjoy, things that aren't always completely palatable at first.
I feel it was necessary to discuss/defend something I enjoy quite a bit. I'd also defend any other genre, possibly just as much, even if I don't actively listen to it (like modern country, R&B, dance pop). While you may dislike rap quite a bit, you're at least trying to say so intelligently, rather than in non sequitur equations. What you said didn't come off as "I don't like rap and don't have any logical reasons for coming to that conclusion, so I'll try to be cute and silly. *raspberry*" I'm not trying to make people LIKE any kind of rap, just sticking up for it amongst a flood of "Yeah, I hate rap, more Muse/Linkin Park!"
I'm also not questioning your having black friends, or saying that all black people have to love rap. I just like to think outside of race when it comes to personal taste. Someone who says they love all rock/metal could enjoy Metallica AND Living Colour (though Metallica would easily come out ahead in popularity), but they also might be surprised to know the guys behind "Cult of Personality" are all black.