Oh, the South was traitorous to the Union. By seceding they showed their unwillingness to follow track that the country was taking. I just find the word "traitor" to be unhelpful because of how malleable and relative it is.
No, the North went to war to preserve the Union the (traitorous?) South sought to break up. Ending slavery was a positive outcome. Which has some irony if, as you suggested, the South was secure in its use of it.
America was founded off of philosophical ideas from enlightenment philosophers. The Constitution is the law, but there are deeper concepts surrounding it.
If you want to call secession as treason, then you must blame the North for the 'treason'. It was the North that caused it by not supporting the South's Constitutional rights. By not treating the South equally under the Constitution. Secession is not treason.
Nothing wrong with the word 'traitor' as long as you use it correctly. The South didn't break up the Northern states. The union still existed. The Southern states simply removed themselves from it. And, behind the 'glorious' excuse to preserve the Union, was money. Ah yes, the motivated greedy yankee.
'Deeper Concepts' ? You mean like this? "When in the course of human events, it becomes necessary for one people to dissolve the political bands which have connected them with one another, and to assume among the Powers of the earth, the separate and equal station to which the Laws of Nature and of Nature's God entitle them, a descent respect of the opinions of mankind requires that they should declare the causes which impel them to the separation." If the north was interested in 'deeper concepts, why didn't she let the South go? Hint...the answer has already been given. Not deeper concepts....deeper pocket.
America was founded first on Reformation Bible believing Christianity. By the time of 1776 you will find both, Reformation and Enlightenment thinking in the formation of America.
Good-Ole-Rebel