Hot take: slavery
You get to say slavery taught people valuable skills *if* you're, say, Roman, 'cause the Romans knew how to exploit people *efficiently* and it was part of how.
You definitely *don't* if you're a Confederacy apologist, because their form of slavery excelled at cruelty, malice, and general fuckheadry while simultaneously being pure goddamn shit at the actual exploitation part.
(Smells like Dark Kantianism, but is probably just our special kind of literally incredibly stupid.)
Hot take: slavery
If you're going to throw all ethics aside and try to recreate the glory of some historical culture complete with the nasty bits, at least pick one that *succeeded*.
We may still have to fight the neo-Mongols or the Tamerlane Recreationists, but at least it won't be so embarrassing that our nemeses are a pale imitation of what was a shitpile to begin with.