Great Q - it is an evolutionary drive to attract a mate which in our culture has gone nuts..
The whole premise is that men especially are attracted to a fertile/non-pregnant/non-diseased female, hence why hip/wait ratio, slim but not size 0, shiny hair etc are all appealing..
But here is the madness, with the likes of plastic surgery, someone who has a nose job for example still has the genes for large noses and so has just created the ILLUSION of being a certain way, their offspring may still inherit large noses and because we are all obsessed may well grown up self-conscious because of it..
Women are programmed to compete for a mate, they do this by trying to be the best looking, female fertility is finite - hence the looking as young as possible etc but this competition was usually on a small scale (like a village) until photography, tv, cinema, net etc all took off, now women have to and do feel the need to compete globally.
This explains why almost all women feel they or parts of them are ugly - who can possibly match up to an ideal - even women who for a short time are attractive get older, or lose that so beauty is really transient.
As you say though, if we all lived on a desert island or could not see then it would expose how silly it all is.
Advertisers though make money from people's insecurities and any female mag has ad's every second page with a perfect model for some cosmetic, perfume or other ALL with the underlying message 'You are NOT ok as you are - buy this..'
Women I feel as well as being illusionists, are more and more treated as decorations and so I strongly believe although we are no longer chained to the kitchen sink we ARE chained to the bathroom one now instead..
Sad. I used to be the same - I would not go out without a full face of make-up and the whole nine yards, these days I am so minimal it is not true and yet I have never felt more attractive or more confident.