It is ironic. Yes, people have a legal right to use offensive terms toward others. And people have a right to ask others not to use offensive terms. What’s so confusing about that?
If one wants to make an argument that an individual or an organized group shouldn’t attempt to influence others’ speech ... well, okay, make the argument. But it has nothing to do with anyone’s Constitutional rights.
In a way, though, I understand some of what is going on here. The left has been waging war on speech for a long time. Much of this is found in their PC insanity, which they take to an absurd degree. This causes a reflexive pushback on our side to anything that sounds remotely PC. The pushback is automated at this point. Frankly-—while I do think that the n-word just crosses so many lines that it should transcend the day-to-day battle of PC vs. freedom-—I do at least understand the impulse to push back. In most cases, I share it, but not this.