It is a fairly common belief that secession is legitimate in cases where it is necessary to stop human rights abuses. There is a somewhat less common view that secession is legitimate if it is supported by a majority or supermajority of people in the seceding region, as long as it does not create human rights abuses in that area. (See, for instance, Christopher Wellman on the matter, and Ilya Somin’s discussion relating to Crimea.)
However, what about the possibility of secession creating human rights abuses in the country which a region is seceding from?
Here’s an example: suppose some of the more anti-slavery Northern states in the U.S. had seceded in the decades before the Civil War. (There was some support for this, since many Northerners viewed the Fugitive Slave Act and wars fought for the expansion of slavery as unjust.) Suppose then that it had swung the remainder of the U.S. in a pro-slavery direction. Perhaps some results could be the expansion of slavery into the West, or more strictly enforcing the Fugitive Slave Act in non-seceding free states.
Could one then argue that the seceding states have an obligation to stay in the Union and keep pro-slavery policies from taking hold?
My current thought is that, since it can be very difficult to predict the outcomes of any given secession, a seceding region should not be blamed for these kinds of issues occurring.
In the previous example, it’s also quite possible that the remaining U.S. would have difficulty expanding slavery into the West without Northern military support. It’s possible that the Fugitive Slave Act would be weaker, since escaping slaves would be closer to permanent safety. (Getting to, say, Wisconsin, is easier than going all the way to Canada.)
Nonetheless, it does seem like this question could pose some issues for deciding when secession is appropriate, both in mainstream and less-mainstream theories. Feel free to post your ideas in the comments.