You made some good points, however you’re wrong about the potential for a food crisis. First off, much of our produce and grain (outside corn) comes from outside the US. If we lost domestic corn and soybean production (the primary crops of the flyover region), meat and most highly processed foods would significantly increase in price, but vegetables, nuts, bread, pasta and other simple foods wouldn’t be greatly affected. Secondly, farmers are enslaved by massive debt, and much of that debt is owned by banks in the communities farmers are a part of. Thus, if they “opted out” they would be destroying their local economy.
I do agree that massive tax evasion movement is a very real possibility. This could lead to rural folk chasing IRS agents away, which would be exacerbated by local law enforcement refusing to protect them. The result would be state level law enforcement being called in due to pressure from the Federal government. This could result in a popular backlash in those states that prompts an active secessionist movement.
If we do see an active secessionist movement, I highly doubt it will end in civil war. Nobody wants to see Americans killing other Americans, the popular backlash across the country to any sustained military action would be massive and unequivocal. More likely, we would see a fracturing of the United States into a commonwealth of nations. The seceding states would retain a relationship similar to the one Canada and Ireland share with England.