Evolution wise, this is because people like in others, what they wish they had for themselves. Likewise, people hate in others what they dislike about themselves. We celebrate the beautiful because we wish we too could be beautiful. We mock the ugly/short/gay/fat/skinny/weak because those are qualities that we ourselves do not wish to have. If all of society punishes those with these traits, people with these traits will be less likely to reproduce and pass these traits on to future generations. Nature is as always, brutal.
But because we humans have emotions we try to hide these discriminations and pretend we don't have them.
I always thought it was interesting how women with self-image issues are comforted on talk shows and told "honey you are beautiful just the way you are!" in one episode then "oh my God you look so much better!" after they get a makeover in the next episode. Not to mention the irony of women in the crowd (who will spend hundreds of hours each year putting on makeup, doing hair, bleaching, & plucking) clapping to the tune of "you're beautiful just the way you are".
My angry bitterness comes from the fact that my whole life I've been lied to. I was a cute kid but after puberty it all went downhill. I was the first to realize it. I was hoping the world around me would keep it's promise of treating me nicely because after all, "it's what's on the inside that counts". Yet, it was all a lie. I've had friends tell me I was ugly, I've had friends tell me they initially didn't want to be associated with me because I was ugly. I've had people in public say to me (as I'm walking by) "Damn dude, you're ugly". And if I choose to get cosmetic surgery some day, I'll have a whole new group of people calling me "shallow". Why? Because I want to look nice? God I'm just so sick of this bullshit. I don't hate myself, I hate the world that lied to me. People who say one thing, then do another.
The same people who call plastic surgery recipients as "shallow" are the same ones who lie to themselves and refuse to acknowledge how important it can be to look nice and feel good about yourself. How happy the millions of people who get surgery every year feel when they have a nose straightened out or a wrinkle removed or hollow cheeks filled.
People tend to believe lies that make them feel good rather than accepting truths that make them feel bad. I'm glad I live in 2013 when I can change the way I look so I can have a better life instead of lapping up all that "it's what's on the inside" bullshit so many people keep spreading so they can look empathetic and modest in front of others.
My Point: I'd like 3 things to change in our society:
1) No more lying. No more "We're all beautiful" rhetoric. No everyone is not beautiful. That's bullshit. Let's be honest. A few people are beautiful, most are average, many can be unattractive, and some are apparently repulsive enough to instill feelings of negativity in others. Beauty can also be subjective so there's a bit of give here and there.
2) To be more understanding towards people who are unattractive by removing the stigma that comes with being unattractive. Aka don't treat us differently. Example: All my friends are outcasts, people rejected by others because they were unattractive, too fat, too skinny, too black (Nigerian descent). Despite me admitting that many of my friends are unattractive themselves, I was still their friend. I was never embarrassed to be their friend or be seen with them.
3) To not look down on people who want to better themselves through cosmetic surgery. Cosmetic surgery is still looked down upon by many people. If you take a leave of absence for 2 weeks and come back with a different face your co-workers will respond negatively. To redefine oneself is what makes humans human. Stop judging cosmetic surgery by looking at extreme examples like Dolly Parton, Joan Rivers, and Michael Jackson. Those are extreme edge cases. Walk into any plastic surgeons offices and ask for their before/after books. Most surgery is meant to leave the patient looking natural not unrecognizable.
For instance: http://www.drrichardjoseph.com/photos/jaw-surgery.php Are they shallow for looking better?