You are missing an important point.
The southern states hid behind “States Rights” to protect slavery. By claiming that black Africans weren’t truly human but less than 100% human, they tried to prevent the Bill of Rights being applied to what was an economic necessity in their region.
You are exactly right. We have a God given right to life,liberty and the pursuit of happiness. The right to liberty trumps state’s rights to deprive someone of liberty.
‘economic necessity’ is a fiction. Those in power int he South wanted to continue the wealth building via slavery, but slavery was not an actual necessity to building wealth if the lust for same was not pushed but anticipated over a longer time period. It is akin to the current leftist crap about ‘doing the jobs Americans won’t do’.
They weren't very good accountants and they didn't understand economics. They never really appreciated the full cost of owning the slaves as a productive unit of the cotton industry. And they didn't understand that the gin had rendered the slaves uneconomic.
Slavery was a dead institution within twenty years whatever happened in the war.
No they didn't. They believed in their right as a state to have slavery and felt they had the right to secede and do what they wish. If there was another issue they disagreed with the North about there would have been the same result. It was all about states rights.
You are missing an important point. True enough that the Southern states made such a claim, but you leave out the fact that the northern states accepted it and operated government under such a premise.
Any and all northern pretense that they held/hold some superior moral high ground evaporates once you realize that everything the South did before the war was also done in the north or condoned by the north. Their opposition to expanding slavery had nothing to do with pity for the slaves and everything to do with maintaining superior political numbers (power) over the South.
Debate the particulars all you like, but never forget that there were more slaves under the Stars and Stripes than there ever were under the Stars and Bars. Keep you misplaced moral snobbery to yourself.