So the consensus is that an attempt at secession, even a democratic one, would result in a brutal military assault?
I think people in the US hear "secession" and immediately think about the Civil War, neglecting how the "Confederates" seceded and then immediately declared war on the United States.
While I think secession from the United States by a state government needs Congressional approval to be technically legal, I do not think such an attempt would immediately be met by force from the government in DC. (Unless the federal government is run by Donald Trump, or someone else who governs by whim and rejects feedback.)
Personally, my biggest issue with Texit is that it appears it would be done only because the seceding government wants to democratically stay in power and be free to abuse the people of Texas.