Five of the original seven confederate states, and eight out of 11 total confederate states did not enter of their own volition. They were allowed to join. Admitted only with the consent of the other states. Shouldn't leaving have required the same?
Your point is valid as are most any on this subject, no matter which side you argue for. IMHO it all came down to failure of leadership....on both sides.
A short answer to your question is yes, leaving should have required the same consent. But, IMHO it was a matter of free will. And this is but one part of where leadership,representing both sides, totally failed.
Consider the state of Arkansas as just one example. Arkansas wanted to remain neutral and non-violent and also wanted to try to preserve the Union. But, the Union ordered the State to send troops. Arkansas still requested a neutral position but that was not a viable stance according to the Union. It was at that point that Arkansas was literally forced out of a neutral and non-violent position. The Southern states were not demanding anything of Arkansas and would have allowed them to remain neutral.
So many factors one can ponder when considering the totality of the War, eh?