Is it also a "chilling effect" that you shouldn't call a black person the N word? Doesn't seem to have chilled anything in rap

It certainly has downstream chilling effects. The lingo around how to describe minority groups is fraught with landmines that often lead to avoiding discussion in general. Growing up in the 90's I remember trying to learn the correct terms for Native Americans, people of color, etc, and for many years I believed mistakenly that some terms were taboo when they weren't (I thought it was rude to refer to someone as "Mexican", for example) and to this day I am still hesitant on some things; is using "Black" as a caucasian offensive in some contexts, wait what's the correct term for the indigenous peoples of the arctic North America, etc.

So when time comes that we might discuss a subject that touches on these groups, I generally tend to avoid it. I think I know the right term, but on the 5% chance I say something offensive then it's a huge negative outcome for me. No I'm not going to accidentally say the n-word, but sometimes it's easier to avoid conversation on the topic if I'm in a context where I may stick my foot in my mouth.