and that applies how?
Follow the thread. You said "Thank God our founders had no such difficulty with the legality and moral obligation for seceding from a tyrannical government. Or we would still be slaves of Great Britain."
Leaving aside for a minute that that was the right of revolution against a government that didn't represent us and not secession from a government that had won the votes of the majority of voters, there are some times when we definitely wouldn't say "Thank God" for the right of a state to secede from the rest of the country.
During wartime, would it be a good thing for one state to simply walk away from the country? Would we praise the Lord for a few states walking out on the debts that we'd accumulated together and on our troops in the field?
If you aren't willing to tolerate state secession on demand during wartime when the country itself is threatened is secession at will a right? If you are willing to accept secession when the nation is fighting to defend itself, then what becomes of the country?