It's legal to use the n word in the US as far as I know, but I think harassment probably isn't ('spamming' sounds like harassment), that's where the balancing act is. Now, it is not legal to throw the n word at someone in most European countries. Hence why I said that these platforms need to filter on a per country basis for all countries they want to operate in.

As I said, Twitter and other major platforms have become de facto utilities and it's no longer a valid argument to claim that as private businesses they are free to do as they please because they yield too much power.