Yes, it was horrible. Yes, it was reprehensible. No one is denying that. But let's not pretend that it was only the Southern states in the United States that engaged in it.
To assume that just because those states attempted secession over slavery that they'd also be sympathetic to the Axis powers is to deny them any sort of nuance. It also ignores that by that logic, all of the countries I mentioned earlier should also have been Axis powers.
So please, go argue semantics somewhere else.