IMHO, in virtually all communist (atheistic) countries and many dictatorships, the living conditions are roughly the same as slavery for all but the ruling elite.
That is, in all countries whose political philosophy is based on the theory of evolution...
Yup. As for the reasons to oppose slavery, aside from "I wouldn't want to be a slave," which is essentially the Golden Rule, there's a very good economic reason. I posted this almost a year ago:
In Toqueville's splendid "Democracy in America," near the end of the book he is taking a slow boat-ride down the Ohio River. He described what he saw along the Kentucky bank and on the Ohio bank. This is in the 1830s (and obviously before the Civil War).
Ohio was hustling and bustling. Kentucky was languid and pastoral. Toqueville observed that on each bank of the river there existed the same climate, same soil, same people, same language, same religion, same everyting -- the only difference was that Kentucky had slavery. He brilliantly concluded that in Ohio, work was honorable, and men were out there, building and hauling and getting things done; while in Kentucky, work was that "they" did, and gentlemen were supposed to follow leisure persuits (hunting, gambling, wenching, etc.), so Ohio prospered while Kentucky stagnated.
Reading Toqueville was the first time I realized that not only was slavery bad for "them", but it was bad for "us" too.
Vaclav Havel said that when he was put in jail, he felt more of a free man than when he was outside. Carlos
It's making a comeback in much of North Africaalthough for a while starting in the mid-19th century -- largely at the behest of Dr. David Livingstone -- slavery was stifled in North and East Africa.
Livingstone was the explorer of Stanley & Livingstone fame -- and a very devout Christian missionary.