I mean, I think there are plenty of ways to put prejudice into a fantasy world, but it should always be well-considered and not done gratuitously. The biggest thing to remember is whatever you put in has to be justified by you and not the fiction.
To some extent I agree. At the same time, some of these discussions get to a point where I feel myself questioning why the fiction exists if it is to serve no tangible purpose.
Certainly, as I've said previously, I do not believe game design is a curtain behind which prejudiced producers of content should be allowed to hide.
At the same time, is there logical validity to illustrating how a differently-functioning fantasy world approaches day-to-day life? I think so, but that view appears to be offensive to some.
Do I think I would be prejudice against Tieflings? No, I don't believe I would be. When I look around the table at people with whom I game, we're honestly sorta weirdos in comparison to societal norms. So, I'm pretty open-minded to hanging out with folks who look, live, and love differently.
Can I understand how/why people in a fantasy world might be suspicious of a demon-blooded person -in a world where demons tangibly exist and go on murderous rampages? Yeah; it's not a default position I would have myself, but I can understand it. That's a situation fictionally created using hypothetical elements of beings which are said to have no choice but to be evil; to me, that's a very different set of circumstances than "these people look and speak differently."
Do I believe there are/were producers of content who use the veil of fantasy to explore their prejudiced ideals? Sure I do. I don't even need to look to fantasy gaming to see that. I can turn to certain "news" stations and see it.
Do I believe that a writer incorporating elements of prejudice into a story containing demon-blooded people proves they are some sort of -ist, -phobe, or so-on? No. Maybe they are, but I do not believe that is a reasonable default assumption right out of the gate.