"... preceded the births ..." is a bit of an understatement. The whole world, for all of history, had been practicing slavery. Abraham had slaves. Aristotle had slaves. All the noble Greeks and Romans had slaves. Slavery existed in China, in Africa, and among the natives in North and South America. The truly amazing thing is that we don't practice slavery today. The founders created the country that brought this about. They should not be condemned, but praised to the skies.
Anyway, the founders tried to deal with it, as best they could. (For a clue as to how difficult this was, imagine trying to abolish the practice of hiring people and paying them an hourly wage. Some jackass 200 years from now may condemn us for having hourly employees -- oh the horror! -- yet it's a standard labor practice in our own time.)
The Constitution actually abolished the slave trade. True, they put the effective date 20 years in their future, but they did it, and it was all they could do. In their own time, it was an amazing step to take. They believed the system would eventually die out. Or maybe they tried to believe it. As much as we look back in horror at slavery, it must be admitted (at least by my standards) that the founders were the best men who ever lived.
Very good point. Sometimes I think, given the essential support of the Free-soiler movement in the Old Northwest (which included Mostly Honest Abe), that the anti-slavery movement had about it something of a Full Employment Act, given the tendency of slave labor in antiquity and in the South to create economic inequality and drive freehold farmers off the land.
You can't make a case in finance or economics against bond slavery: what the world needs, every industrialist and planter alike would have told you 140 years ago, is a good five-cent human being.
Hence the Free-soilers were correct to worry about the possible introduction of cotton-resuscitated, slave-powered agribusiness into areas where they wanted to go, like the Nebraska Territory. In Texas, historian Fehrenbach has recorded in Lone Star, his manual of Texas history, slaveowners like Jared Groce, who accompanied the Old Three Hundred to Texas in 1820 and 1821, were able to use their bondmen to stake out much more acreage than the freeholders under the Spanish land-grant rules. Each slave was allowed to stake out a holding, which then inured to his master -- how that worked, and why the Spanish sat still for it, is a minor mystery to me still. But that is how the planters in Texas, whether accepting mercedes from the Spanish Crown or, later, staking claims under the Republic, were able to put together very large parcels of "peach-bottom" or prize bottom-lands, and achieve the economies of scale that the freeholders both North and South rightly feared. Only in the South, the wrath of the freehold, hardscrabble farmer turned against the black bondman, not the Man in the Big House.