最近的是texas vs. white, 想独立： 1). Revolution -- 推翻现有legal regime; or 2). Consent of states.
从现实角度来说，consent of states几乎只有理论上存在的可能性，即使congress通过也有法理上的问题。
你说的'州不能通过州内投票独立'正确，'即使全体公民投票通过也不行'很难说，但most likely correct。
"宪法就是这么规定的" is very misleading and confusing. Should be: "that is how the supreme court interpreted and widely accepted by american people"