Howja think the demented duck and his ilk would have fared THERE?
Of course, the slave count wouldn't matter since the slaves were originally freed by Executive Order - not a Constitutional Amendment.
So Lincoln could just expand the reach of that EO to cover the entire United States, and not just the rebellious areas under military control.
Then when the Union replaced the state governments of the former Confederate states, they could have made it illegal on the state level.
Same with women voting.
Actually, it wasn't until after the Constitution that women LOST the ability to vote.
https://en.wikipedia.org/wiki/Timeline_of_women%27s_suffrage_in_the_United_States
(kinda ironic, no?)