[uncommonsense]

"I never understood the idea that somehow a war decides a constitutional question. Since when does OVERPOWERING the other side mean you are constitutionally correct?"

By using Scalia's logic, another civil war where the succeeding states won - would settle the question in the affirmative - yes it is legal.

[Still Thinking]

By using Scalia's logic, another civil war where the succeeding states won - would settle the question in the affirmative - yes it is legal.

That's exactly right. If the secessionists won, history would view their acts as legal. In the Civil War, the anti-secession forces prevailed, thus settling the legal question, till the next time.