This applies to both RP worldbuilding and story-writing, and has already been done (probably better)
here.
So incredibly often I see settings that are clearly not historical, but set in some romanticize, fantasticized past, a "here there be dragons" sort of a place, with corrupted, vaguely rose-tinted versions of the sexism, racism, ablism, homophobia, and other discrimination that ruled in the corresponding time period of world history. "It's historical," creators too often shrug when asked why. "To omit those aspects would be unrealistic." Or sometimes, slightly more justified but wait no not really, "Utopian societies are unrealistic." News flash: If we do ever get rid of discrimination, there will still be societal strife from different sources.
"Unrealistic." Your main character's dating an elf, he has a magic sword and a hyper-intelligent flying horse that doesn't need to eat and you're saying you can't cut the discrimination of the time period you're supposedly emulating-- because it would be
unrealistic.
Bullshit. Is it really that hard to imagine a society without those issues?
Now, plenty of good writers do include discrimination in their societies, but they
treat it realistically, as the complex problem that it is, and show its effects. They show how
it gets into all facets of society, not just as a few jokes made by less savory characters, or a few incidents of ill-treatment. They don't just treat it as an excuse to have characters be horrible to whatever group. They show that
no group is perfect, depict everyone (not just the good guys) as people, and don't use the tired, rotten trope of the hero high on the societal privilege ladder saving his poor simple minority friends who can't help themselves. They don't apply the rosy filter of "but it was the good old days" to it. And of course if the setting is actually historical and properly researched-- medieval Europe or imperial China, for example-- historical accuracy is a legitimate answer. "Alternate timeline" settings may also pass, depending on what ways they are alternate in.
But if it's not portrayed as a complex problem, and hasn't got any real basis in history to be true to, I really don't see why it's necessary.
This is probably not the last you'll hear from me on the subject; future posts may go more in-depth.
Writing rant disclaimer:
Some of you may have read some of my fiction or participate in an RP I am part of. If you notice that something in my writing has something I have labeled as a problem in my rant, go ahead and tell me so! I may not have noticed that I'm doing whatever it is, so that can help me! However, I do want to keep this place polite, so please no unnecessary bashing of my characters, or, for that matter, anyone else's, be it a fellow commenter or a fellow RP'er.
Blog note: You might notice the "Frustrations" label. "Frustrations" posts are usually going to involve a fair helping of my opinion and social commentary. Keep this in mind, and feel free to disagree in comments, but do so civilly, please.