Of those 15, it might be illuminating to know how many did not on grounds of principle versus merely that the cost/benefit didn't favour it for them at that time?
Slavery was a controversy from the beginning that finally bubbled over into the Civil War. It was not, as this question seems to imply, a near universally approved of practice where a few just didn't happen to need slaves.
That doesn't justify allowing it for almost a century. The US was comparable to the rest of the West, in this regard. The final abolition of slavery in Britain wasn't until 1833.
That doesn't justify allowing it for almost a century. The US was comparable to the rest of the West, in this regard. The final abolition of slavery in Britain wasn't until 1833.