The southern constitution allowed secession. The confederate congress would most likely have been quite mild for that reason after the war. The prospect of secession is after all the only real check on central government power.
Where? Read the preamble and it says "We, the people of the Confederate States, each State acting in its sovereign and independent character, in order to form a permanent federal government..." That doesn't look like they were will to let anyone go.
The confederate congress would most likely have been quite mild for that reason after the war.
Let's not look at 'most likely' but instead let's look at what they did. Davis and the confederate congress ignored the requirement for a supreme court and the prohibition against protective tariffs, enacted conscription and forcibly extended the enlistment of the state militia regiments for the duration of the war, seized private produce without compensation 'for the war effort', forced private ship owners to reserve a large percentage of their cargo space without compensation 'for the war effort', conscripted slave labor without compensation 'for the war effort', nationalized industries like salt and liquor, suppressed newspapers, enacted martial law in cities hundreds of miles from the front, proposed confiscatory taxes, and that was in the first 4 years. Doesn't bode well for the future, IMHO.