Okay, I was going to directly quote @surreality responding to me, but the thread's moved on and it would be just chopped up anyway, so instead I'm posting a few thoughts.
-I don't think there are limits to what art should explore, if done in a considered and respectful fashion by someone who earns that trust. (If it's badly handled, the creators can and often do catch flack for it.)
-I think RP, with people I trust to be sensitive and thoughtful, should have no fewer restrictions put in place.
-I think a MU* environment, for several of the same reasons I love the MU* environment (fast, loose, messy collaborative storytelling with complete strangers) is an absolutely terrible setting to foster the sort of sensitivity and trust that it takes to bring the sort of real-world hate and slurs into the fiction.
-I think that banning in-character slurs is a reasonable restriction to foster player comfort and inclusivity, in the same way many MU*s ban in-character rape. Yes, it happens in real life; no we do not want to deal with it.
(-I don't think "son of a bitch" or "motherfucker" are in any way equitable with racial or homophobic slurs in this context.)
-I think that talking about how aspects of real-world discrimination resembles aspects of fantastical racism ignores that most of the complaints are in the vein of "hate speech against groups I'm a member of is disruptive to my fun time."
-I think that, say, a cowboy MU* is less likely to be a thoughtful expression of American race relations in the 1870s and more an excuse for people to pretend to be awesome gunslingers in cowboy outfits, and setting a "you must be this white/male/straight to be awesome" bar is not a good look for inclusivity in the hobby.
-I think that, while some degree of historical accuracy is a concern, the activities of one in-character month in our hypothetical cowboy MU* have a good chance of overshadowing the collected lifetime achievements of any real western gunfighter, and I also think that people would object if TS in the cowboy MU was required to focus on a cowboy's saddle sores, BO, and dickcheese, historically accurate or not. I think allowances can be made.
-I think that, with what I see across the hobby of the people arguing that it's beneficial to use slurs in-character versus the people who express discomfort toward their use in-scene, it starts to feel like a bunch of us white straight folk talking about how real we keep it while alienating minority players from the hobby.
That's just my thoughts.