Dudes who set up RP universes that are heavy in racism, sexism, homophobia, etc all in the name of "being realistic hurr hurr hurr".
This is a case of someone failing to communicate the real reason for their decisions. Which is very common, though it's not always as bothersome as this. You're not including these things because they're realistic, you're including them because you want them to exist for the inherent value they bring to the story. It's a matter of tone: if you want a dark, gritty fantasy world, this is one way to get there. The sense of realism is just a peripheral benefit.
Of course, there's also the people who use fiction to push a political agenda. Fuck those people. But in my experience, it's rather hard to differentiate with certainty whether the beliefs of someone's character / setting are their own real-world beliefs, or just flaws to make the character / setting more interesting. As long as they're not openly preaching misogyny OOC, that is.