Perhaps it’s because we don’t want to lower ourselves by talking like trashy people. I am just fine with “n-word”, “f-word”, “s-word” etc. when I have to reference something said by vulgar people.
That’s an interesting point. However, I believe your line of reasoning would tend to leave people who don’t want to lower themselves unable to discuss our culture in a coherent way.
An additional problem results from the poor vocabularies and weak spelling skills of many modern people. The “unsayable word” (or untypeable word) concept tends to ooze all over, so that words such as “niggardly” and “negate” provoke crises, while “Niger” and “Nigeria” can set off software intended to limit us to “nice words.”