Manumission

Infidels like to raise moral objections to Christianity. For instance, they try to tar Christianity with the evils of slavery and racism. By way of comment:

i) You have slavery under secular regimes. Stalin had forced labor camps for his public works projects. 

ii) Of course, when an atheist does it, fellow atheists assure us that that has nothing essentially to do with atheism. But why not? 

Even if, for the sake of argument, we say that Stalin's policy wasn't motivated by atheism, there's still the question of how an atheist is in any position to condemn it. From a naturalistic evolutionary standpoint, why is it wrong of human animals to enslave members of their own species? 

iii) There's also the question of how to interpret the historical record. Let's take some examples. From what I've read, the first slave code in South Carolina was enacted in 1690. It was oppressive and unjust. However, it's striking to consider what it didn't regulate. It didn't outlaw manumission. Then the code was amended in 1712 to outlaw the manumission of the children of white men and slave women. And it was not until 1841 that a general prohibition against manumission was enacted. For 150 years prior, that was permissible under some circumstances. So this is clearly a rear-guard action. 

This means that even if a master wanted to manumit his slaves, he no longer had the authority to do so. The law didn't recognize the status of his emancipated slaves. Likewise, the perceived need to enact these laws presumes that whites had to be prevented from emancipating slaves. In that case, you can't just assume that any given white Southerner was racist. For if they all supported the institution of slavery, why these belated laws to eliminate loopholes in the system? Clearly, some were undermining the system by releasing their slaves. 

On a related note, atheists may think the anti-miscegenation laws were motivated by theories of white superiority. To safeguard the purity of Aryan bloodlines. But from what I've read, the anti-miscegenation laws were originally designed to protect slavery. The children of slaves were slaves. But what about the children of slaves and a white mother or father? Since white parents were free, would their children be free? From what I've read, the purpose of the anti-miscegenation laws was forestall that dilemma. As such, anti-miscegenation laws ironically expose the morally arbitrary nature of race-based slavery. And Jim Crow-era anti-miscegenation laws reflect the same motivations and internal tensions. They prohibit white behavior as much as black behavior.