I don't really see how liking to watch bunch of students getting murdered one by one by serial murderer or a monster, or trapped and tortured by some sicko like in Saw movies, is that much different from liking NTR. Or Saw fine, but Human Centipede bad? There is continuum of suffering in many media of entertainment and art, and it's not that convincing to say that this fictional suffering is fine, while that fictional suffering is bad. Are people even allowed to root for bad guy protagonists, like Bonnie and Clyde, or From Dusk till Dawn, or Overlord LN/anime? I didn't enjoy "From Dusk Till Dawn" since MCs brother was rapist-murderer, and decided against Overlord once I've heard what cruelties MC's side commits later, but it shouldn't mean it's wrong for other people to enjoy it. Or to like adult-high-schooler age-gap romance. We may get into rather prudish territory here, where every story and character is graded on being moral enough to pass.