> there are significant racial differences between slaves and people, and the same rules do not apply to white ones as to black ones because they are not the same species, they do not have the same brains/possibilities/rights/etc. Just like they did not grant any freedom to animals or trees.

Personally, I find it hard to believe that Southern whites, who lived in such close proximity to their slaves, actually believed this. It sounds like convenient bullshit that you would try to tell yourself in order to justify what you are doing. You see these people everyday, you speak to them, you own generations of them, and they raise generations of your own children in your house (mammies). Of course you would see enough to know that they are the same species and every bit as human as you are.