I see you are as obnoxious and mannerless as ever. Only an boor would start a communication as you did. Apparently, you are another bumptuous jackanapes who gets his hands on a manual of logical fallacies and convinces himself that he can refute every argument he doesn't like by sticking a logical label on it. Would that life were that simple.
My point was that we can say now that communism or fascism or nazism wouldn't last -- that they were internally unstable or contradictory and doomed to fall apart. This didn't help people in 1939 or 1947 who had to figure out what to do about aggressive dictatorships. It didn't help them much to think that "sooner or later" such ideologies would die out "on their own." And indeed, the "inevitable" collapse of repressive regimes was largely a result of the fact that people took a stand against them.
So it is with slavery. Someone's idea now that slavery's decline was "inevitable" means little to people in the 19th century who saw slavery growing ever stronger. If slavery collapsed it had a lot to do with people who acted against it. You might want to look at Time on the Cross and other works by Fogel and Engerman to see how some scholars question whether slavery really was dying out. In any case, people at the time didn't know that slavery was "dying out" and weren't wrong in thinking that what would happen depended very much on what they did and didn't do.
You might also want to take another look at the work by Thomas Kettell that you refer to. It's not good economics, but Kettell's argument is that slavery was economically strong and that the American economy depended on it. Not a good work to cite if you believe that slavery was on its way out.
Hummel's argument is too clever by half: let the South go and runaways from the Confederacy to the North would make slavery uneconomical. But it's one of those off-the-wall, counterfactual conjectures that it's impossible to prove or disprove. And really the contention that the Confederate states wouldn't or couldn't do what was necessary to prevent large-scale slave escapes, when they'd been organizing slave patrols and pass systems for years is pretty flimsy grounds for an argument.
Consequences do matter. People judge the consequences of Lincoln's actions. They judge the consequences of the means he used. Yet some people simply assume that the Confederacy equals freedom. They don't look at what the Confederates were after and what their victory would mean. They also aren't very curious about or critical of the methods the rebels used or what they would mean. They simplistically identify secession with greater freedom, but that's not the case. They also assume that once you declare that you are oppressed you can do as you like, and that's not a responsible approach to political problems, either.
I mentioned that not everyone believed that secession was a right before the Civil War in order to counter another widespread assumption about the era. Not only Lincoln, but Buchanan and his Attorney General Stanton believed secession to be unconstitutional. Even Robert E. Lee, early in 1861, believed unilateral secession to be against the Constitution.
It was a widespread view of things. What the government could do if a state declared itself to be outside of the union is another matter about which people disagreed, but it simply isn't true that everyone accepted secession as constitutional. I don't argue that this "proves" that secession was unconstitutional, but it does controvert claims that "everyone" or pretty much everyone believed in a right to secession.
People disagreed about such matters. If there was any consensus about the matter, it wasn't that states could leave the union whenever they wanted to. That's something not enough people realize. Questionable arguments about this or that state having discussed secession in the past don't change how things were in 1860.
If an amendment isn't ratified it isn't a part of the Constitution. If an amendment was thought necessary to allow for secession it's clear that those who supported it recognized that the Constitution did not unambiguously allow for secession. That's pretty simple.
The real vote on this was procedural and closer. It was the vote on whether to have a vote. Once the procedural vote was lost, some Congressmen changed their mind and supported the resolution. At about the same time Congressmen dealt with your proposed amendment they unanimously voted for this resolution:
Whereas the Constitution of the United States is the supreme law of the land, and its ready and faithful observance the duty of all good and law-abiding citizens: Therefore--
Resolved, That we deprecate the spirit of disobedience to that Constitution wherever manifested, and that we earnestly recommend the repeal of all statutes, including nullification laws, so-called, enacted by State legislatures, conflicting with and in violation of that sacred instrument, and the laws of Congress made in pursuance thereof; and it is the duty of the President of the United States to protect and defend the property of the United States.
Congress was confused at this point, striking out in different directions to try to resolve the crisis, so I don't think your proposed amendment is the ace in the hole that you appear to think it is.