I don't know, would you also agree the other "insoluble issue" was state's rights? If every Southern slave had been freed, and then the South had seceded, would war have happened anyway?
The reason that states' rights was so important to the South is that the area they wanted to exercise their rights in was that of slavery.
Or do you think they would have seceded just to prove they could?
My point has always been that the North and South gradually drew apart emotionally, until many in the South no longer felt the "ties that bind" to the Union. The issue that created this distance was that of slavery.
Secession was in many ways like a divorce. Few people get divorced just because they believe they have a legal right to do so. They get divorced because they want OUT for some reason. The reason they want out is the root cause of the breakup, regardless of what rationale they may come up with to justify their actions.