It’s like many entanglements in vice. There is such a warpage of conscience and defensiveness of evil, that it can not come undone overnight.
The original constitution shouldn’t have allowed slavery. That was a very poisonous pill for the new America. You can’t be trumpeting independence before God while denying some of His creatures the independence that He wants them to have. Not without inviting retribution.
Had it not protected slavery, the Southern states would have broken away in 1787 when the Northern states would not have been able to stop them.