Idk, I have been called ugly, and my theory is that there's different kinds of ugly, imagine it on a spectrum. While I get suspicious too, some people really are just ugly like...a house elf, or in the way that people perceive older women to be unattractive. Aka, invisible (which, yes, might be an advantage).
Also it's sometimes other juxtapositions; i.e., invoking a sense of righteous rage that...really has nothing to do with that woman. Look at how vicious and cruel people can get over ugly women having confidence or having nice things; over at trufemcels a femcel reported that a bunch of otherwise nice and normal normies were just viciously making fun of an ugly woman pictured with a awesome car. There's a projected sense of "undeservedness" many people naturally perceive when they see ugly women with nice things, or being happy. There's been femcels that report actually, almost paradoxically, getting insulted more when they try. I.e., people ignore them when they're in tomboy mode and only start getting grossed out when they try to be more feminine.
Note: some say forms of disgust involve the "perversion" of the familiar or desirable, and the visceral rejection of thus...so, you can be blandly ugly or morbidly so. Not saying this applies to everyone but it's food for thought.