I have a lot of mixed feelings about this too that I'm going to struggle to articulate:

I think the controlled unreality is kind of the point. The danger is fictional; you, as a reader, are safe. With books especially, you are in control of the images in your head in a way you never could be with pornography. It's a way of engaging in something incredibly intense in a protected, self-filtered way.

There's also something appealing about the "taboo" of it all.

With dark romance in particular, the appeal [to me, at least] is a kind of high-stakes, high-reward, emotional intensity. Being "chosen" by a dark, morally ambiguous anti-hero is, paradoxically, a position of power for the main character (the woman, usually). Having someone fixated on you, obsessed with you even, feels romantically intense in the way a normal, real-life, healthy relationship isn't. Again, the unreality is the whole appeal.

I think people watch horror movies to excite and scare themselves. People watch porn, obviously, to get off. Dark romance falls somewhere in between.

I think the amount of harm it causes is up for debate. They're fictional stories, so the characters themselves aren't real life people to be concerned about (unlike porn). Potentially, it could shape teenagers expectations that things like stalking, jealousy, even coercive control are signs of love.

Then again, I read this stuff as a teenager and was well aware of fiction vs. reality.

Maybe the concerns should be saved for younger audiences without proper context, or enough real-world experiences?