It's an incorrect bottom line.
It is not like the 1860s era republicans were a benevolent lot and let Confederates off the hook out of the goodness of their hearts.
They didn't. Johnson did.
The Confederate states were not trying to overthrow the government because that would be treason.
They entered into armed rebellion and warred against the government. That is treason.
They just wanted out of a union they voluntarily entered, like a divorce.
A divorce requires a judicial ruling to become legal. Using your analogy the Southern states walked out if the marriage after having run up the credit cards and grabbing every bit of community property not nailed down on their way out.
It is only common sense that states should be able to leave a union they voluntarily created and many people believed that at the time.
With the exception of the original 13 they needed permission to join the Union. Shouldn't leaving require the same? Walking out and abandoning responsibility for issues like debt and treaty obligations while lifting every piece of property they could without compensation is a plan guaranteed to end in acrimony. Which was probably what the Southern states wanted all along.
The Confederate States territory was invaded. They didn’t so much enter armed rebellion as simply defend themselves. You can post as much B.S. as you like but the reason that no Confederate leaders were tried for treason is because both sides knew it wasn’t treason. It wasn’t lack of opportunity and it wasn’t benevolence, it was because the government knew they would lose the case if they brought it.