While I understand your view, I disagree about the secession being illegal aspect. It was a Union of states. Even today each state has its own legislative sovereignty. That’s why we still have states that are commonwealths and have their own constitutions. That’s why states can override the federal laws such as Colorado and others legalizing marijuana. A state can vote to leave the Union. If it was a Unitary government, you would be correct about the secession being illegal aspect, but this country has always been a Republic. Which gives a measured and balanced focal of power equalizing the states with the federal. They can vote to leave if they so choose to. Doesn’t mean the federal government has to like it as was the case with the Civil War.