Because parasocial relationships with ewhores isn't healthy, particularly at a stage in their life when they should be forming real relationships with their peers.
I hear this claim from the pornsick but I’d like to see all the studies backing it up.
... and before you haul out crap from BYU or whatever, be aware that some of us have actually read that work and know how poor it is.
Are you saying that the intersection is uniquely bad? In either case limits to content made in an effort to minimize parasocial relationships cut across very different lines than if the goal is minimizing access to porn.