Traitors to the United States of America shot first. Your non-answer answers to the inadequacy of your understanding and the fundamental untruthfulness of the Lost Causers about their cause.
Your argument about a standing army is not germane. The land on which Fort Sumter stood was the property of South Carolina. When South Carolina voted to secede, it declared its borders sovereign. The garrison at Fort Sumter then became an invading force whose presence could not be tolerated.
There is no provision in the Constitution forbidding secession. However, there IS one enumerating the powers of states where the Constitution does not explicitly assign those powers to the federal government. So if anyone was treasonous in the sense of ignoring constitutional constraints, it was the Union.
And as much as my “non-answer” disqualifies me as a further conversant, I have not resorted to name-calling or personal attacks on your integrity.