Slavery and Productivity

My friend Michael Barnett made this observation recently:

I hate this argument that slavery would have ended naturally without the Civil War because slavery is economically unproductive. No, it’s not. It is very productive which is why it’s had to be outlawed one way or another in every place which has forbidden it.

Great point. He put into words something I’ve thought before too. The argument against slavery has to be a moral one.