Well actually we do not agree. Slavery was not why the original 7 seceding states left. It was merely the legal pretext. We know this because they turned down the Norths offer of slavery forever by express constitutional amendment if only they would return.
Obviously the Upper South only seceded when Lincoln chose to start a war to impose a government by force on people who did not consent to it.
There is another matter you are overlooking. If you trace along the northern border of South Carolina starting at the Atlantic Ocean heading west and trace that border all the way west and south until you encounter Mexico just west of El Paso you will notice that is a border that is over 1500 miles long. There is simply no way that border could have been secured - especially without modern technology back in 1861.
Had the original 7 states been able to leave in peace, they would have been a foreign country not entitled to the protection of the Fugitive Slave Clause in the constitution. All any slave would have needed do was cross that border into the US and theyd have been free. Secession effectively would have meant the end of slavery. None other than Lincoln made this argument many times. Nobody could refute it.
Slavery was dying in the Western world by 1861. Most everyone knew that. In the places where it still survived, its days were numbered. The whole all about slavery argument was bad federal propaganda put forth in 1863 when the federal government was desperate to justify the bloodbath it had started, and revived starting in the 1980s by PC Revisionists in Academia to serve their Left wing politics.
Dred Scott apparently missed the memo on that. So did the southern states who cheered on the Supreme Court TRAMPLING "states rights" and FORCING northern states that did NOT allow slavery to comply with a slave owner's "right" to keep their slaves regardless of where the slave goes.
Slavery was dying in the Western world by 1861. Most everyone knew that. In the places where it still survived, its days were numbered. The whole all about slavery argument was bad federal propaganda put forth in 1863
I agree that slavery wouldn't have lasted, but somehow those rascally Federal propagandists managed to get the seceding States to include their propaganda in their secession documents promulgated in 1860 and 1861. You have to literally close your eyes to the reasons declared by the secessionists to argue they didn't leave because they sensed a Federal threat to slavery after the election of a President from an abolitionist party.
It's downright Orwellian to say they didn't leave because of slavery when they said they left because of slavery.
Again, that's not the reason Lincoln invaded, but it is the reason they left.