Experience appears to teach that many people exhibit a kind of moral cognitive dissonance according to which they express moral repulsion toward some behavior (usually historical), together with approbation of some other behavior that is in many ways morally similar. At present, this most commonly takes the form of moral approbation or tolerance of abortion coupled with a denouncement of various other historical activities such as nineteenth-century slavery or the activities of the Nazi regime.
My hypothesis is that the contradiction is not true cognitive dissonance regarding a moral principle, but rather a consequence of apparently moral judgments being based on something amoral in nature, namely social mores. Our cultural rejection of the Nazi regime is more a social phenomenon than a moral one, which is why we can at the same time revile it and nod approvingly at contemporary eugenics movements. In general, people will tolerate any sort of behavior that does not violate prescribed social norms. In other words, we are fundamentally amoral. Our putatively moral principles are derived not from natural or divine law but from custom. And so we should not be surprised that perfectly ordinary and otherwise decent people can so easily be deluded into accepting the most vile moral outrages. There are a great many people who, though at present they would never dream of supporting the reinstatement of the peculiar institution, would quickly flock to it and find all kinds of rationalizations for it were it to come back into fashion. The same can be said of almost any other behavior whatsoever.
Perhaps this is an obvious truth, but it was only relatively recently that it occurred to me in these terms.
