There were, as a matter of fact, condemnations of slavery in the ancient world, specifically in early Stoicism.
Anyway, where does this belief come from that moral beliefs are transhistorical and abstract? If the objection is that moral beliefs are ultimately contingent, well, yeah. So what? All beliefs are ultimately contingent.
BTW, this bit
"But even within capitalism social practice eventuates in the establishment of allowable and not allowable economic activities"
does not work at all, because there is no reason a priori to prefer an allowable activity to a nonallowable one. Regardless of the economic system.
> Carrol Cox
> --------------------------------------------------------------------------------
> There is no transhistorical basis for the condemnation of
> slavery, and
> moral condemnations of Roman or Greek slavery have no
> basis. (It is
> worthwhile noting that even ancient slaves, apparently, did
> not
> condemn slavery as such but only resisted their _own_
> slavery.)
>
>