There is no right of secession?

To those who say there is no such right (as in the Southern states). Are you saying that once a body politic has joined itself to a larger body, it has no right to leave that body, for the rest of the history of mankind, no matter how brutal or immoral or repressive that government becomes, even to the extreme? Is that what you are saying?  If you do not say that, then by default you grant that the right of secession does exist, and your argument with the Southern states is not that they did not have the right to secede, but perhaps that their judgment in the particulars in that instance was faulty.