Anime

Why is it that human characters that have threatened killing, or have killed in the past—Ubel, for example, happily tests out her destructive spells on people—are given complexity and understanding, while demons have not? Did we not also evolve from beasts?

The author seems very eager to leave the context of the fantasy world and draw comparisons to the real world, as if all fantasy has to be social commentary at the same time. The demons in this world are effectively aliens, tailormade in every possible way to be enemies of the other intelligent races. Why do they need complexity or present a nuanced moral dilemma? We've had that same exact setup just as many times as the "plainly evil enemy". It's a weird claim to me, that Frieren would be improved in any way by turning the demons into yet another plot twist about how all of this was really just the fault of humans or a grand conspiracy or whatever. The point about this being used to make a convenient punching bag in game-like settings to level up the heroes, doesn't apply to Frieren either. Almost every confrontation against demons starts out humanizing them in some way, only to show how that is a misinterpretation of their outward appearance and empty words. It really hammers home the point that humans are incredibly susceptible to empathizing with anything that looks like one, which is exactly what makes them so dangerous and skilled at exterminating them.

Despite inviting us to empathize with strange and threatening mages—and inviting us into the headspace of an ancient elf who experiences life fundamentally differently from us mortal humans—the story doesn’t extend the same grace to demons.

The audience is constantly invited to empathize with demons, even if it doesn't yield the expected result of a troubled, complex, but ultimately human character that the author is looking for. In my opinion.

Frieren: Beyond Journey’s End plays with the always evil race trope but doesn’t fully escape it.

Frieren plays with the "bad guy actually turns out to be relatable, maybe we can all just get along :)" trope very successfully.