Nier got it in one. Models are sup[posed to be clothes-horses. It's not about being 'attractive'; it's about not having any inconvenient curves that spoil the line of the clothes. Similarly, they're often not stunningly attractive girls facially speaking; the agencies look for bland-looking girls whose faces can take on any 'look'.
The issue of thinness being touted as the only way to be attractive, successful or anything else in our society is something that fashion contributes to, but isn't entirely to blame for.
And, it's unfair as unfair to hate on thin women as it is to hate on fat ones. Every woman is a real woman, whether she's fat, thin, or in between. The 'unreal' women are the manipulated images we're increasingly seeing all over the place, where even women who are already considered among the world's most beautiful are subjected to computer tweaking to make them 'perfect'.
And, Erisad's also right. A lot of people have a lot of money invested in the business of women (and more and more these days, men) never looking quite good enough. If we all just stood up and said No to self-hatred, No to diets, No to airbrushed models, No to judging people purely on appearance, and Yes to the real, varied, deep beauty and value of all of us, the whole edifice would crumble overnight. And if even one person turns against it, it makes us all stronger.
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"Grunge? Isn't that some gross shade of greenish orange?"