Atheists becoming less unpopular?

[Neo-Scholastic]

I quoted Saint Thomas' reply:

Reply to Objection 2. Considered absolutely, the fact that this particular man should be a slave rather than another man, is based, not on natural reason, but on some resultant utility, in that it is useful to this man to be ruled by a wiser man, and to the latter to be helped by the former, as the Philosopher states (Polit. i, 2). Wherefore slavery which belongs to the right of nations is natural in the second way, but not in the first.

This echos Justinian's Institutes in which it says, "slavery is an institution according to the law of nations whereby one person falls under the property rights of another, contrary to nature." Slavery belongs to the "right of nations" as a legal mechanism to impose punishment for wrong-doing. Slavery is NOT based on natural reason. Or as Aquinas says immediately proceeding the part you quoted "The right of nations is distinct from natural right" Thus he makes the distinction between inherent natural rights and the justice system that protects them.

So it is clear, human beings do have divinely created existential equality and as such inherent rights as part of their essential nature. These come from God. In contrast to this, the "right of nations" does not come from God but was allowed by God in the ancient world to accomodate a world corrupted by sin. As a legally imposed punishment people can loose those rights and become slaves, almost without exception in situations where one would otherwise have died*, according to the laws by which their nation is governed. To this day our justice system takes away the rights of convicted criminals. Being given a life-sentence for murder is a modern luxury and is in its own way just another type of slavery.

*The Egyptian sociologist  'Abd al-Wahid Wafi faced the same problem within Islamic tradition. He lists the conditions under which slavery got imposed in the ancient world. He concluded that slavery was in some sense a practical legal substitute for execution resulting from crime (like unpayable debt) or military slaughter.