There's a range between checking everything and checking nothing, though. If you're writing a portrayal of a particular real-world culture that you're expecting people to portray in their games, is it really too much of a stretch to bring in someone from that culture to look it over and make sure you haven't accidentally included some bad assumptions?
This isn't about the activity of the group, though. My example was specifically about what was written into a setting by that setting's author. And if that material turns out to be hurtful to someone, it isn't in the act of roleplaying it that they feel that hurt - it's in the act of reading it in the first place. That can't be undone simply by walking away from a table.
Again, this isn't about what anyone at the table did. It's about what the writer of the supplement did when they wrote it.
I personally don't think its necessary, at least in the context of a fantasy world which, by definition, does not include real-world cultures. Even if it does, or cultures closely derived from real-world cultures, I have no issue with the author creating their own version of it. It doesn't have to be accurate to reality, and is just a take--even if a pejorative one. That is part of the freedom implicit in the creative act.
Now I don't have to like it. I have the right to be offended or find the portrayal to be problematic. But because I believe in artistic freedom, I'm not going to try to censor it or get rid of it. I don't have to read it or run it at my table.
There's also the problem of "bringing someone from that culture." If I'm writing about a fantasy version of the Incan Empire, who do I consult? A modern Peruvian? If I'm doing a wuxia setting, do I ask my Chinese friend? What if he or she knows little about ancient China? And of course there's the matter that wuxia itself is fantasy, not a realistic depiction of a real-world period or culture. At a certain point it becomes rather absurd.
A fantasy world is its own thing, with its own internal logic that has nothing to do with our world. If a fantasy race is completely evil, it only needs to make sense within the context of the fantasy world. If I were writing a story set in our world, I'd definitely want to do my research about whatever I'm writing about.
As for reading something and being hurt, this is where we run into the problem of trying to adjust everything that may offend anyone in any way. Where do you draw the line? Some people are easily triggered and believe the solution is censoring or getting rid of that which offends them, when the core issue is rooted more deeply and won't be solved by such actions.