What were the southern arguments in favor of secession during the civil war?

Answer 1

Pretty much the same ones found in the Declaration of Independence. The Union government was placing heavy tarriffs on manufactured goods to force them to buy domestic, but wasn't doing the same for agricultural products, so that the northern mills could buy from overseas.

The real question in the South wasn't "why don't we leave" but more of "why the heck do we stay? It's not like the Constitution was irrevocable."

Oh, and don't be suckered into thinking slavery had anything to do with it. They already had that, and no one was talking seriously in congress about abolishing it. Slavery didn't come up as an issue until two years into the war.