Why do people expect equality? Where has this unnatural expectation come from?

Religion emphasizes common humanity. Christianity in particular emphasizes the common state of sin in which all human souls exist, and during the Medieval period, Christian jurists, drawing on Christian, Platonist, and Stoic tradition, developed concepts of equal rights. As liberalism evolved out of Christian theocracy, the idea that "all men are created equal" took hold in the minds of many during the Enlightenment. Of course, this doctrine was not an explicit claim that there are no differences between people, but as liberalism spread it had to be recapitulated in each individual mind, and this led to the theory being watered-down and made crude, such that people now simply talk about "equality" instead of, say, "equality before the law" or "equality of rights."