That's just bravado. Mostly. I suspect that serious support for a modern insurrection would depend upon the circumstances. There are many things that the government does now that I find deplorable, but none of makes me want to take up arms against the government. Things would have to be pretty severe in order for me to support a war against the United States. What if a fascist regime took control of the three branches of government and our liberties, even basic ones like free expression and the right to peaceably assemble, were outlawed? What if the government systematically targeted some ethnic groups, say Arab Muslims, and put them into re-education camps? I don't think I'd support a rebellion based on regionalism alone, and clearly a majority of Mississippians don't either. I think that is what the 37% of Mississippi voters in this poll are supporting. That is more just obstinacy--call it Southern Pride if you want--than anything else.
