I am not going to come on here and tell all the people who think they are plain or ugly that they aren't- perhaps they are. But if you walk about any town or city centre, and look at the people, unless you are in a posh part of London or LA, most people are quite plain or ugly. The amount of beautiful people, truly beautiful people, is really quite small. You will also notice that many of these plain, ugly or overweight or otherwise imperfect people are walking with their partners, their kids, they are having meals out, going abroad, working in good jobs and so on. They are not all hiding indoors-and rightly so, you do not have to be amazing looking to live a happy interesting and worthwhile life because millions do have these lives, even whilst being not the best looking.
There's also a category of people, into which I definitely fall, which is 'people who make an effort'. You can decide if you can be bothered to be in this category, with chosen clothes, make-up or just being clean and tidy. That's your choice and you don't have to be beautiful to be in it. People do appreciate people who 'make an effort' even if they don't want to bother themselves. If you don't want to bother, don't, but you can't say you can't be in this category because anyone can.
I agree that society treats people who are beautiful differently, but there's not so many of those- if you 'make an effort' you can achieve pretty much the same effect, that's my approach anyway.