I’m fairly sure that skin hasn’t always equaled sex, and biologically, a shoulder is not processed in your brain as “I want to have sex with that.” The very first human beings were not excited by a knee or an ankle even. But as we entered a society that viewed women as property, woman had to cover themselves. The idea of sluttiness is tied to the idea that your virginity as a woman is the most important thing about you, and that you are basically worthless without it. Way back when, even before miniskirts were invented, women who had pre-marital sex were not good enough to be married off to a respectable or successful man, because she was not respectable herself. The pureness, and respectability of a woman was measured though chaste clothes, to show that you haven’t exposed yourself to anyone except your husband. And as the centuries wore on, even as pre-marital sex became a social norm, the value placed on virginity is still prevalent. A woman’s value is placed in her “purity”, by wearing clothes that are revealing she lowers herself to being impure, to being a slut.