It depends on whether you believe all people are actually "human beings". I am referring here to the practices of slavery in the US and elsewhere, where it was perfectly acceptable to kill, rape, torture slaves because they were not deemed to be completely human, they were deemed to be inferior beings. The same is true for how the first European settlers in Australia regarded Aborigines - as savages, something less than human. So it is a bit of both, an exercise in oppression but it also boils down to social/cultural elements regarding how different people should be regarded and treated, based upon their characteristics. In this regard there are no absolutes - for example, it was immoral to rape a free white girl but not a black slave. Killing a child was immoral, but not killing an abnormal child, born to incest. Killing, stealing from and raping Jews was actively encouraged in times gone past, but not killing, stealing from or raping Protestan Christians. Moral standards are applied differently because of some subjective characteristic which defines different people as either "in" or "out" in terms of their humanity and inherent worth.