You know, I appreciate this sentiment, but I'll tell you, I've twice in my life (and only in the south) met people that gave me a bit of pause on jumping on this. Both were young white men who threw around the N word and general racist and racial language in conversation. And in both cases, I later met their best friend, who was a black guy. Not just a buddy, but like literal best friend, call each others' mother "mom", camping together type friends.
I'll be the first to admit I didn't get that, and still don't. Those things are incompatible to me. And to be fair, this was more than ten years ago, where there might have been a little more nuance about how people thought that word could be said by whites. But still...to me that's totally incompatible. But it did give me a little pause about getting on my high horse to necessarily lecture someone from my high horse right off the bat. I wouldn't participate or laugh or encourage it, but probably wouldn't jump all over them until I knew them a little more.
However, that's different from witnessing racial harrassment of somebody, where I definitely do think stepping in is called for.