I’m not sure I would have agreed with that amendment. I don’t see the problem with a state withdrawing if done properly and within the bounds of the Constitution. Unilateral secession as practiced by the Southern states did not fall in that category.
The Constitution says nothing of the sort, as I'm sure the senators knew. You seem to be saying that states could secede but only with the permission of states that might be: (1) taking advantage of them, and/or (2) not living up to their side of the constitutional bargain. What state would have agreed to that kind of restriction?