I'm asexual, and if I were pretty I'd have a lot more trouble. I have a nondescript sort of face, two inch long hair, and some extra weight... I blend into most crowds (until I move or talk, anyway, and then everybody thinks I'm weird!).
I'm trying to lose weight now, because you are more likely to be hired if you are skinny; but it's difficult and I keep thinking, "If I'm pretty enough for people to want to date me, how will I be able to tell them I'm not interested, even if they're wonderfully nice people?"
If you're not very pretty, people seem to be more interested in friendships than romance. And if you want friendships, you may be better off if you look plain than if you look pretty.
I don't think I'm "ugly" but then I've never seen anybody I could describe that way unless they'd been injured or hadn't had a bath. It all depends on whether you are comparing people to some ideal, or whether you're looking at them without expectations... This is more of an artist's view than anything, unfortunately; many people see only what is accepted as beauty, and everything else as ugly, when really there are a lot of different ways people can look.
It probably helps that I am faceblind (I have a lot of trouble memorizing faces), so that when somebody looks unusual, I am more likely to remember them.