-Shouldn't be censored because of right to free speech (1st amendment). People have the right to listen to whatever they want to listen to, and create whatever music they want to listen to. To censor it would be restricting their constitutional right to express themselves.
-It's good because it has good beats and rhythms, and a good bass. A good, steady bass (especially if it's relatively slow like in most rap songs) can affect your heart rate, and slow down your blood pressure and help you relax. Studies have been done where people listened to songs with a certain bass beat for a long time, and their heart rates slow down and beat in time with the music. So rap could even be used for medicinal purposes, to help people with high blood pressure.
I wouldn't put that it's good because it created African American millionaires, because
1) there are non-African-American rappers (tons of them), and
2) the fact that they became millionaires from it is not necessarily a reason that rap music is good or shouldn't be censored. People get to be millionaires doing all sorts of naughty/illegal things too (like selling drugs, prostitution, robbing people, and hacking bank accounts).