Second, please point out the wording in the Constitution that declares secession illegal. I can't put my finger on it.
Third, the South WAS in favor of the expansion of slavery into the territories but that was only one of the reasons it seceded. The North, however, DID NOT go to war to end slavery. It wasn't even on the list. Lincoln went to war to preserve the union.
"The North, however, DID NOT go to war to end slavery."
It was not the only factor, but it certainly had something to do with the war. I agree that Lincoln went to war to preserve the Union, and the slavery abolition was a sideeffect that could possibly be viewed as a political move to solidify support in the north and to establish a moral highground in the eyes of the world. It worked well.
"The founders did not want an all powerful central government and took great pains to prevent it."
They did not want an all-powerful central government, and I don't recall stating that they did. But they wanted a central government that was more powerful than individual states. Under the Articles of Confederation the federal government was weak. The founders wrote the new Constitution because they felt that we needed to strenghten the federal governmnet in order to survive as a nation. Under the new Constitution states could no longer print their own money or impose state-to-state tariffs.
Secession was secession from the Constitution. That is what it was. The Constitution formed a union. The seceding states broke the union, which in its self was a violation of the constitution.