I'm a white american and I think I agree with this. Making sure that only one race of people can say bad words on the internet doesn't seem practical to me. If we don't want some races saying a word, I don't see a way of preventing that which doesn't sacrifice either anonymity or black people being able to say that.
There's only one implementation that I can imagine, and it's pretty impractical and ethically dubious. The idea is to have some kind of verification process to prove that you're a certain race, and somehow publicly store the public keys of people in each category. Then, when someone want to post a word that only some races can say, they submit a zero-knowledge proof that the message was written by someone who controls the private key of one of the public keys in the appropriate category. But I'm pretty sure that a registry of people organized by race is neither practical or desirable.
Nevermind the fact that art such as film frequently relies on the use of slurs when dealing with this subject matter.
We aren't protected in real life from being called words. I've certainly had my fair share hurled at me. By having to deal with it both at a young age and in adulthood, I've grown a thick skin and strong defense system.
I worry that this attitude is more dangerous that what is trying to be accomplished.