The thing i don't like about how demons are written is that they're perfectly logical and then just can't after a step or two.
They're so full of hubris, like they simply discarded a few hundred possibilities without a second thought, and didn't even lay the groundwork or the most basic lessons you'd keep in mind doing a project like this.
If you want to feel or copy an experience, you must actually undergo the same experience, or similar enough experiences. The fact they wanted to study humans and have emotions like humans without ever going to the trouble of "creating a credible threat to their life" is just such a massive oversight on the demon's end, like, what were you doing all those centuries ago? sleeping? if you don't feel like you're gonna die how tf can you guarantee you'll learn the same lesson as a group that constantly recognizes they will die one day? Either the desire is fake or the demons are stupid.
How the fuck are you gonna say "i'm gonna feel X when I die" when you haven't been wounded in god knows how long??? Death outside your control is literally a non-concern for any of you mfers, how the fuck do you have the hubris to assume you'd understand just by looking?
The fact a demon never once asked themselves "what if a random demon just starts killing all the humans by accident" and at the very least say "erm. that couldn't happen... right? right???" with some doubt, it's just funny. I don't know how they did their fancy magic development without any of these kinds of considerations, was it pure luck?
It's just peak "you had too much fucking leeway and that's why the shit you're doing sucks ass now" that hyuse rags on in World Trigger's newest chapters. But that's because neighbors actually face a credible threat to their lives.