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.