Is this a possible use of 'CEV?' So far as I understand CEV, it's not possible that it could change: our CEV is what we would want given all the correct moral arguments and all the information. Assuming that 'all the information' and 'all the correct moral arguments' are constants, how could the CEV of one society differ from that of another? The only way I can think of is if the two societies are composed of fundamentally different kinds of beings. But the idea of moral progress you describe assumes that this is not the case.

I don't think violence has declined. State violence has increased. Further, since we are imprisoning a lot more people, looks like private violence has increased, supposing, as seems likely, most of them are being reasonably imprisoned. Genghis Khan and the African slave trade cannot remotely match the crimes of communism. And if it has declined, Xenophon would interpret this as us becoming pussies and cowards. Was Xenophon more violent and cruel than any similarly respectable modern man? Obviously. But he was nonetheless deservedly respectable. We rightly call the ten thousand brave, not criminal. Social acceptance of brave, honorable, and manly violence has greatly diminished, and so brave, honorable and manly violence has greatly diminished. But vicious, horrifying, evil and depraved violence, for example petty crime and the various communist mass murders, has enormously increased.