In 1790, every existing state, save for Masachusetts and Maine (which had been part of Massachusetts) permitted slavery. Even then, slavery was a predominately southern institution. For instance, in 1790, black slaves made up over 60% of South Carolina's total population, and 40% of Virginia's population. However, in the next 60 years, up to the 1850 Census, the North was extremely successful in ridding itself of this evil practice. In 1850's, several political events hastened the eventual conflict between the States. And by 1860, in the North, the practice of slavery was nearly extinct.
In 1790 there were 694,000 slaves.
In 1820 there were 1,500,000 slaves.
In 1830 there were 2,000,000 slaves.
In 1840 there were 2,500,000 slaves.
In 1850 there were 3,200,000 slaves.
In 1860 there were 3,800,000 slaves.
Even after the prohibition of slave imports around 1800, the slave population was growing exponentially.
Your analogy is absurd. Let me pose another. Is a reformed drug addict morally superior to a practicing drug addict? Most people in the south did not participate in the slave trade; however, the powerful landed Southern elite were slave addicts in the worst way. They brought the South down because they were morally decrepit and were unable to muster the moral courage to do the right thing.