You don't see just a little bit of difference between the Constitution and your church?
The fact that a voluntary club practices limited admission does not in any way imply that the club has a right to put a gun to the head of dissatisfied members to force them to stay
If permission is required to join why shouldn't leaving be the same?
Or do you think that churches should have the right to threaten their parishioners with violence if they decide to take their worship elsewhere?
A very poor analogy. For a more accurate one how about a business contract? Would it not make sense for the protection of all members of the partnership to prevent one member from unilaterally breaking the agreement?
My church has its own constitutions. Which is why I'm able to see an analogous situation -- we're discussing two constitutionally-organized entities.
If permission is required to join why shouldn't leaving be the same?
Because Freedom of Association necessarily implies Freedom of Disassociation. No contract allegedly requiring permanent membership and/or requiring permission to leave can be validly enforced unless that contract specifically stipulates permanent membership and/or the requirement of permission to leave. In private society, any limited-admission club that tried to claim that members who wished to leave had to jump through certain hoops not specified in the membership contract, would be laughed out of court.