So, because they said, "We're going to commit treason," before they did it makes it not treason? Sorry, but allowing unilateral opt out of government by any individual or group makes government meaningless. So, saying, "You're not the boss of me!" first doesn't alleviate the charge of treason.
I'll grant, that makes George Washington and all the other founding fathers guilty of treason, too. But there is a huge difference between committing treason and rebelling in self defense of freedom to live your life, and doing so because you want to continue committing brutal crimes against your fellow human beings for the sake of the profits. In the antebellum Southerners' minds it may have been phrased, "I'm rebelling for my freedom!" But their myopic focus on the "my freedom" part doesn't eliminate or excuse the implied, " to treat my fellow human beings as property, to split up families through the sale of human beings, to brutally beat them to enforce their obedience, and otherwise deny them their freedom."
Short version: treason can be a justified rebellion if the state is committing crimes, it's just treason when done to continue committing crimes.