In the case of the Civil War Smedley Butlers speech applies. For what it's worth there was some division within the south even among the Generals themselves as to the South's direction and intent. That division and some jealousy from those who had Jeff Davis's ear cost the south the war. Jeff Davis also like Lincoln became too focused on the industrialist namely the cotton industry rather than the intent of the founders and states rights. At least one CSA general told him as much was a thorn in Braggs flesh. :>}
You may have been had.
For a lot of people the Confederacy was a bunch of neighborhood guys -- good ol' boys meeting in a garage -- who decided to fight the power and take on the Man.
In many cases, they were the power and the Man. Certainly many East Tennesseeans tended to think so. They trusted the federal government more than they trusted the wealthy planters of the flat lands.
Maybe the 20th century would give their decendants reason to think they'd made the wrong choice. But one has to compare the two alternatives and their consequences, not what actually happened to some imaginary utopian scenario.
But if the state assemblies passed a bill of secession and the governor signed such it should have been recognized as a lawful withdrawal form the Union.
Many or most East Tennesseeans certainly didn't think so. And think back on how things were at the time. Davis and the fireeaters were doing all they could to force the results they wanted. In one state the referendum required to ratify secession never took place. In another the result never has been reliably established. There was violence and threats of violence. It wasn't all a neat and clean measured process.
And what happened after ordinances of secession were passed (and often before)? Property was seized. Supplies and weapons were stolen. Debts renounced. Forts attacked. Even if secession were legal, that left a lot of questions about debts, agreements, responsibilities, obligations, settlements, and federal property. Davis's answer was to pick up the gun.
I don't think you're neighbors were wrong to oppose the rebellion, even at the risk of being attacked as rebels themselves. Keep on reading, and learning, and you may be surprised at what you discover and come to believe.