I'm not a huge rap fan, but most of what people judge their opinions about rap is based on what they see and hear in the commercial industry, which is just what you've all said, BS, crap, not music, oxymoron, and other things like violent, pessimistic, depressing.
Anyway, that is rap, but there is hiphop as well, and although i not a big fan of this either, I recognize that that of it which exists beneath the mainstream is significantly better both musically and lyrically. Hiphop and rap are both more about the lyrics than the music, which is why you could better call it, angry, offensive, rhyming poetry to a drum beat. I have heard good hiphop with good messages that was not so offensive on the whole.
I personally can't stand any of the new stuff. It's so copied and UN-original, I want to cry. Any rap or R&B from a woman is pretty-much the worst though. Musicians though, these days,(for the most part) are not about how people hear their stuff, but how people see it; they skip in the music dept. since this is the hard one, and attract people through the visual gimmicks and so forth.
About Maryln Manson, or however you spell it. This person is perhaps THE most intelligent musician in the mainstream, at the moment, in my opinion. He is extremely smart with captivating his audience, and generating a following. The shock-appeal is just that, and every bit of "bad publicity" he receives, he appreciates, for it makes him more popular and more seen. His message is not what people see it as: the death, drugs, satan, sex, anti-christ stuff. That's the shock appeal, which I think he used in the beginning to develope his personna for the purpose of becoming recognized, and now that he is, we can see that his image shifted to a more retro, glamour-rock look. I don't really care about the image, but he has created some excellent, hard rock and roll, and metal. Also, he had his first band, which is basically the same one now, very popular before they had ever played a single note together, before they had a drummer. He's a master promoter. He's no worse than Sinead O'Conner, and she didn't get this bad a rep.
I can't handle Boston, Rush or Kansas...they all sound the same to me and it sounds like useless guitar intros...