well generally, you get a lot more ugly/unattractive villain characters compared to beautiful villains in stories. it's a really easy (and lazy) way to differentiate "bad" from "good", and a lot of stories take it. for example, voldemort, hannibal from silence of the lambs, nurse ratched, the joker, like 80% of disney's animated villains, the cockroach alien from men in black, etc.

but really, i feel like it's not easy to just simply state "villains must be beautiful" or "villains must be ugly" because their appearance plays a role in, well, their role! like villains who hide in plain sight or seem good while being bad all along tend to be attractive (like norman bates or prince hans from frozen), while villains who tend to be the Big Bad tend to be designed with very little regard with how attractive they must be. but even this isn't always common, and sometimes you can have this switched up.

overall, i can't really agree or disagree with you, because arguing over how villains are supposed to look involves a whole lot more factors than just simply "this character is a villain".