Many of them were atheists and freethinkers and so the leftist climate in the North was much more agreeable to them than was the cultural climate in the mostly Christian Southern states. They all claimed they hated Southern slavery. What they really hated was private ownership of slaves.
-Al Benson, Jr.
http://revisedhistory.wordpress.com/2012/03/27/communism-comes-to-america-earlier-than-we-think/