You overlook the fact that not only was the South paying between 50% and 80% of the entire Federal Budget, (Yes, the Federal Government was primarily funded by slavery) but by forming a separate country, the south horribly undercut Northern Monopolies in Shipping and Tarriff's, resulting in potentially billions of dollars in losses for Northern Interests, specifically New York and Boston. (Where most of the Wealthy and influential people lived.)
Pea Ridge has posted numerous period letters from Northern Interests wailing about their losses of revenue. (The one about New England Businessmen demanding Lincoln DO SOMETHING about their secession related financial catastrophes would be appropriate right about now.)
Of course no one wants to go down in history saying they killed 600,000 people to restore their lucrative businesses and monopolies, so they insisted that it was for a "moral" cause, though if that were their prime motivation, they could have outlawed slavery in the five Union states that still had it. They could have removed the "beam" in their own eye first.
Exactly how was the South paying 50%-80% of the Federal budget? Income Taxes, property taxes,