It's all about the effects of what is said. Fight the Power and Fuck the Police were published when there were no social networks around; The post-2K Web changed everything, and the chances of having more people rioting because some rapper want to become their idol (gigs, books, TV appearances, etc) isn't that dim.

If I wrote a rap song with "stick an artichoke in your butt" and magically a hundred people follow the advice and hurt themselves, someone for sure will at least attempt to censor my song. The imitation problem has been with us for thousands years, but social media made it a lot worse by dramatically augmenting the audience, then moving a lot faster than laws, and allowing some grey zones where a law prohibiting this and that would be too draconian and no law makes similar scenarios very possible. That's where we should be the ones who censor ourselves when we suspect that someone could be damaged by our words. That rapper didn't, because he pursuits fame and money, and Fox News by jumping in his defense acted exactly as one would expect from a source that has nothing to do with journalism.