No the worst type of hentai is the one with ugly as fuck art, AND disgusting themes (scat, torture, guro, mindbreak, bdsm, etc all in one). Like seriously, look at the recent uploads on nhentai, ugh.

I think it's mostly part of a stereotype, or it could just be a fetish. Seems like it has something to do with a beautiful and high class kind of girl being disgraced by a completely slob/disgusting pig sorta thing, bringing her down to their level or something. not that it makes it any better.