Say a State secedes. The State Government is the ONLY government for that State now. There goes the checks and balances. If that State decides that Sharia Law is the way to go (or any other liberty robing ideological rot) then there would be zero recourse for the citizens. There would be no Constitution that kept the State from obliterating our rights. The State being the end all could change their own Constitution into any form that they wanted. Nazism, Communism or any other ism is open season.
You seem to only point to the means to our demise.
I believe the United States is an essential strut of Western and Democratic civilization, that secession would be horrendous for the Union and by extension the world, and therefore I vehemently oppose secession and would see it crushed.
Furthermore I abhor the lingering petty regionalist sentiment that exists in the United States and I'm glad that increasing mobility, immigration, and the like are finally beginning to dilute it.
Anti-Democracy advocate, Mixed government is the only good government
THE second point to be examined is, whether the [constitutional ]convention were authorized to frame and propose this mixed Constitution.