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I think you don't have consider a person an enemy just because they consider you one. So in the case of someone you don't know is conspiring against you, I would say of course they're not your enemy--that's something you have to decide. An outside observer could say they were your enemy, if they were privvy to more information.

I don't think an otherwise ambivalent slave owner is the enemy of his slaves. Oppressor or something, yes--but not enemy. Some slave holders were certainly the enemies of their slaves, though.