If the interpreter sees themselves as a member of a racial group, and thinks that their racial group has ownership over a word, they may get upset if they see an outsider using their word. I understand that. That is what's happening. But the mentality in which someone sees themselves as a member of some separate group because of their race is exactly what I am opposing.
You say our actions send signals. Well, is this guy just drinking water at a water fountain? Is he just sitting on a bus? Or is he sending a "signal" that he thinks he's as good as a white man by drinking from the "wrong" fountain or sitting in the "wrong" seat on the bus? The problem is not entirely within the so-called signal, a big part of it is within the mind of the interpreter.
I know how saying that word would be received by a lot of black people, and I would never do that, as I have a very strong commitment never to harm anyone, and just a lot of general sympathy, compassion, and love for black people. But I have to resist if anyone starts claiming that their race gives them special ownership over words. That is a step in the wrong direction.