I had the same thought. I think its Kinda strange how bad people are often portrayed as ugly in mangas (everywhere in general). My father would say their appearence is a physical Manifestation of their immorality (wtf). Why do people always assume that you have to be ugly to be evil? If she was portrayed as beautiful, would people hate her as much as they do? A predator is a predator regardless of how they Look, it wouldnt really make a difference.
There's this thing called physiognomy, ofc it's not scientific and I didn't agree with this. But it's kinda understandable that your father has that perception. Lots of people do. And you figured out the reason why people often make their villains ugly, because if they were attractive, people will be sympathetic toward them and not really supporting the protagonist. Happened all the time.
Happened even in the real life, like the viral dude who killed a mother and her child, some people really supporting him simply because he is attractive to them like ew.
I really wish female predators weren't always portrayed as fat pig like women because it's pretty tiring watching everyone insult them based on appearance instead of y'know. The actually deplorable characteristics of being a predator and stuff. I know it's not that serious but it still bothers me