I think you mean rappers. Not 'singers' in inverted commas. They're rapping, not singing. If you thought they were trying to sing and failing then I've got around 50 years of music history for you to catch up on. Just because you don't like it doesn't mean they're doing something badly.
And no, it isn't bigotry to say you aren't allowed to use the N word, but they are. Not unless you have a history of being racially abused with that word that goes back centuries to when your forefather were transported on slaving ships across the Atlantic from Africa. An explanation of the differences in context and use when black Americans use the word the word in black American slang - including spelling and pronunciation - is going to be pointless here as you can't even bring yourself to acknowledge a musical art form that's been going for half a century and has roots that go centuries beyond that.
Honestly, I thought we were well past the "why can't I use the racist word when they do!" bit of small-minded tantrum-throwing.