Apologists for American slavery often employ relativistic arguments: Legal slavery was part of human society from its earliest days and persisted in the world for decades after it was abolished here. In some places, it persists even today.
These things are true, and historical context is important. We can’t hold people of the past to modern standards. But we can hold them to their own.
The very absence of the words “slave” or “slavery” from the Constitution speaks to the shame the framers felt. We can grant reality—that the politics of the time meant the debate in Philadelphia in 1787 wasn’t whether the Constitution would permit slavery or not, but rather whether we would have a Constitution or not—but we can’t pretend that it was undertaken without knowledge of the evils involved.
It was an ugly calculation, and it required three key compromises in the document: Anti-slavery delegates agreed to allow 20 years before banning the international slave trade, which was already odious in much of Western society; Southern delegates agreed to get credit for only three-fifths of their enslaved people in determining congressional representation and Electoral College votes; and, most barbarously, the convention accepted South Carolina’s demand for a clause relating to fugitive slaves.