Rick (npub1qw3…qe66) that's not as bad. "Slavery is morally permissible" can have a lot of caveats attached. OK the west supports slavery but only as a punishment for a crime and we avoid the chattel generational stuff and if you don't want to work that's fine, you just won't have extra money for the prison commissary. Or: the Romans weren't monsters for putting the defeated to work instead of killing them. Or: if you isekai into another universe and a series of strange coincidences force you acquire elven and catgirl slavegirls, that's fine man, just be nice to them.
But "slavery is good" is taking it to another level. If something's good, let's have more of it. Let's form raiding parties to acquire slaves, because it's good actually.