Unlike those altruistic Southerners, full of humanity for their chattel property, whom they could whip at will, rape at will, sell papa, or mama or any of the kids if they so chose to do so, when ever they chose to. Those same Southern slave owners that wanted their beloved property to count as a full human being for purposes of representation.
So by all means, feel free to count them as caring one whit about the humanity of slaves.
As awful as it sounds to modern ears, they were valuable property as was their work product. So, envisioning some sort of system wherein such valuable property was routinely killed, maimed and otherwise devalued is overwrought emotionalism.
Recall that slavery had existed since the dawn of written history at the time, practiced practically the world over with the exception being English Protestants beginning in the seventeenth century. The Caribbean Isles had it, South America had it, Africa certainly had and still has it. Can people mistreat their property, even destroy it? Yes and sometimes they did and do. However, to depict this as the normal state of things just flies in the face of logic.
So, those altruistic, pure as the driven snow northerners, planning to ride in on their white horses to save the slaves from the evil southerners, insisted that those same slaves were not fully human for some strange reason. Those same northerners who profited from the slave trade both directly early on, and later indirectly had a mysterious desire to diminish the personhood of black people. Now why might that be? Was it caring about their humanity? No, it was an exercise in political power and they cared not one whit about the humanity of slaves.
See how that works?
How does one explain the docility of a warrior class of people who overwhelmingly outnumbered the plantation owners? Sure, there were a handful of slave rebellions but nothing resembling a general uprising. Conclusion: “slavery” was nowhere near the brutal reality that has been portrayed and there was general contentment.