Well, I mean, for one, states aren't people
For two, the South were being abusive a-holes (ya know that whole slavery thing).
Third, this relationship was multiple states with multiple states. There was no mechanism for disunion. And, again, their stated reason for disunion, slavery, is utterly deplorable and isn't a proper reason for leaving the union (according to the natural law thinking of the time). So, ummm, yeah it kind of doesn't work from start to finish.