I love the double think of a country built on states seceding from another country forbidding states from seceding from their own. "God gave us the right to rebel, but not the right to rebel against us!"
Or, alternatively, "Do you want the Critical Period again? Because this is how we get the Critical Period again." America had seven years of its federal government being essentially optional, and it sucked so much that the Federalists resorted to shenanigans of questionable legality to replace the Articles of Confederation as rapidly as possible with something that established an actual government.
Even if you're willing to pretend that the secession crisis was not about slavery, letting the slave states go uncontested was never an option. The precedent it would have established would have made the federal government optional again; if states could leave whenever they wanted, then they would essentially have veto power anyway. America tried that once and nearly fell apart. It's not doublethink to not want to try that again.
I don't see why I have to pretend that the civil war wasn't about slavery to see the irony of the situation. I mean, I see the double think of the South demanding the freedom and right to self govern over the privilege to keep people from being free, but unlike the first there's not many people in this thread exhibiting that idea so there's no need to post about it.
I didn't mean that. I was referring to the standard neo-Confederate nonsense that the Civil War had nothing to do with slavery, everyone involved was an opponent of slavery, and the only reason the War happened was because of nebulous, generic "states' rights" issues...which happened to concern the legality of slavery.
My point was twofold: one, that given the issue at hand, the precise legality of secession was a secondary concern. Some kind of armed conflict regarding the keeping of slaves was inevitable, probably by the mid-1850s and certainly by Buchanan's presidency; as has been noted up-thread, it was economically vital to the South and intolerable to the North. This was pre-Posse Comitatus Act, as well; at some point, Northern soldiers were going to be shooting at armed Southern rebels who refused to peacefully release their slaves. Secession just made it an actual war instead of a series of police actions. The Crittenden-Johnson Resolution was a transparent sop to Kentucky, Maryland, Missouri, and to a miniscule degree Delaware; secession was a useful way to frame the conflict, but it was never the reason for the war, which would have happened in some form or other regardless.
But let's indulge the folks with Confederate flags hanging on their walls and pretend that this was all about "states' rights" in general. It's still not necessarily hypocritical to assert, on a purely practical basis, that the Revolution produced a (barely) tenable political entity that slave state secession would not. There was no explicit Constitutional proscription against secession, true, but actually letting the South go peacefully would have established a precedent that returned a level of authority to the individual states not seen since the Articles of Confederation and, in fact if not in name, reestablished the vetocracy the Articles had devolved into.
In other words, no matter what reasons the South had offered to justify secession, letting any state go would have returned America to a frankly awful system of government -- and that precedent would stand for the seceding states, too. Whether that's hypocrisy or irony or learning from past mistakes is up to you, I suppose.