If the Declaration of Independence articulates a right capable of overthrowing the thousand year old British Monarchy, it is certainly equal to the task of dissolving their participation in a government that is only "four score and seven years" old.
Apart from that, the US Constitution says nothing on a state becoming independent, because everything that needed to be said on the subject was said 11 years earlier in the Declaration of independence.
The Confederacy were nothing more than a bunch of slave owning plutocrats.
In terms of who was collecting the money from slave production, it would appear that New York City and Washington DC were making more money off of slavery than were these Southern plutocrats.
Yes, I agree plutocrats are bad, but how about we focus on the more powerful and destructive plutocrats in New York and Washington DC that are destroying us now, just as they destroyed the Southern states then?
Oh for Christ sake, go take your meds.