I tried to compute an estimate of the current percentage of the US population that's forced labor vs. at the peak of the pre-abolition slave trade, and from what I can tell, it's currently higher than it ever was back then.
People argue that what we currently have isn't the same or as bad, but present-day prisoners would point out that the current system is a form of eugenics: We keep a large percentage of reproductive-age black males locked up where they can't father or raise children. Back in the slave days, owners often chose who breeded with whom. Both are reprehensible, but you could argue either situation is worse than the other. At least the old policy didn't have the effect of slowly reducing / diluting out the black population.
Anyway, the US should ban slavery.