You're asking about the origin of ethics for non-intellectual, mass society? Our conscience is instilled in us when we're young, so morality comes from indoctrination and thus from traditions. Often, those traditions are religious. In secular Western societies, the morals are typically liberal. The harm principle picks up on the same intuition that religions mean to account for, and that intuition might be hardwired: do unto others, or we should be free to do what we want as long as we don't deprive anyone else of that same freedom.
Part of secular liberal culture, though, is capitalism, and although children are largely insulated from those lessons of realpolitik, we learn eventually that we're in a competition for resources in which strangers merit only minimal respect. We should cooperate where we can, but we should feel free to exploit our rivals' weaknesses to get ahead in life. Capitalism is implicitly socially Darwinian, via Adam Smith's invisible argument. The logic of capitalism is that greed is good: selfishness fuels the competition, which generates innovation. So that aspect of modernity conflicts with the other aspects of the modern welfare state, as I argue at length below:
