The 1860 debate seems to be over the law governing territories, there does not seem to be a specific territory in question or desired for possible Statehood, which was my main point.
"Consider the alternatives: conceding most reasonable Southern men were Unionist before events of 1859-60, what were the options for remaining in the Union and maintaining a semblance of political parity? The House of Representives had long since been lost, based as it was on population. The Senate, designed as body to represent all states equally, was slipping away. Southerners hoped to maintain political power through admission of more slave states by any means possible, and by means of the Democratic Party. The South might be safe if Democrats voted along party lines to defeat the schemes of the Republicans. Beyond a president and supreme court members friendly to slave interests, what did the future hold?"
I agree on all points. However, there was nowhere to go to expand slavery. What you have is a political pressure cooker with no relieve valve. The North, always in competition with its brothers in the South, like a good game of checkers, finally boxed them in, either by design or by fate. The South, unwilling to lose, desperate to save itself, quit the game before losing its last piece.