Yes, the South fired first but it was clearly much more complicated than a simple "they started it!" The North had made it clear they were not going to allow the secession.
This is part of why the South hasn't just dropped it. The war was started, in large part, over slavery but we learned that the United states are no longer united by choice.
This is part of the ongoing argument over state's rights vs federal power. The confederate flag is a racist symbol, but it's also a rejection of federal power over the states. Politics are complicated.
That's the modern, historical revisionist version, but the "state's rights" the South seceded over weren't a rejection of federal power over the states. Their complaint was that the Northern states were not returning escaped slaves or allowing them to take their slaves into states where slavery was illegal, and that the Federal government was attacking their state's rights by not forcing the Northern states to do so. That's not a rejection of federal power. See for example http://avalon.law.yale.edu/19th_century/csa_scarsec.asp
I suspect the revisionist interpretation of state's rights probably comes from the 50s fight against desegregation.
I don't think you're saying anything that disagrees with what I was trying to say. Slavery was most or all the cause of secession. However, after finding they couldn't take their toys and go home the southern slave holding states had another reason to be upset.
It's a bit of a tautology really, but there isn't a conflict between State and Federal powers until there is a specific disagreement. The document you linked says as much:
We affirm that these ends for which this Government was instituted have been defeated, and the Government itself has been made destructive of them by the action of the non-slaveholding States. Those States have assume the right of deciding upon the propriety of our domestic institutions; and have denied the rights of property established in fifteen of the States and recognized by the Constitution; they have denounced as sinful the institution of slavery; they have permitted open establishment among them of societies, whose avowed object is to disturb the peace and to eloign the property of the citizens of other States. They have encouraged and assisted thousands of our slaves to leave their homes; and those who remain, have been incited by emissaries, books and pictures to servile insurrection.
That's what I get for citing Wikipedia. But the idea was also brought up by actual southern politicians, particularly in the discussions at the end of the Mexican War.
And wanted to expand southwards in Mexico, Cuba and the Carribean in order to have a large slave-based empire.