Unfortunately, I think he does...
Can you make a convincing argument as to why slavery is bad? You maintain it's bad and that Gd is immoral for allowing it. So surely it ought to be cinch for you to explain and defend your position.
Actually, I can prove it is immoral simply by pointing out what Jesus said.
"Do onto others as they would do onto you."
Would you want someone to do to you what was regularly done to Slaves in this country. The beatings, the mutilations, the rapes? The forced labor. Being able to sell your children and you'd never see them again?
The Old South was more like
Mandingo or
Roots than
Gone with the Wind, guy.
If you accept that Jesus set a standard of morality that we should all treat each other the way we'd want to be treated, than Slavery is immoral by Jesus' own standards.
Too bad he never got around to saying so explicitly.