A not-so-quick history side note: thought I'd add an interesting perspective.
Most of the "truths" taught in schools are far from it. For example, the Founders debated the slavery issue ferociously. A few Founders argued purely on moral grounds, every human has certain God-given rights, etc. But most of the debate between the colonies centered around the economics of slavery. In the end they were forced to punt on the issue as the impasse held the potential to derail the entire Constitutional Convention. They simply set the issue aside.
The Constitutional Convention took place in the 1780's. By the 1790's an invention would dramatically alter the slavery debate. Eli Whitney's cotton engine (shortened to gin) allowed cotton in the South to be de-seeded by machine. Therefore, fewer human hands (slaves) were needed to prepare a bale of cotton for market. In turn, those in the South softened their stance on the slavery issue for economic reasons. As the demand for slaves diminished dramatically in the South their human hands were increasingly required in Northern states.
Expansion into the plains states meant a great deal more wheat production, which was harvested by hand. Two men swinging hand scythes could harvest about an acre per day. The rapid "taming" of the prairies demanded many more human hands, if only seasonally.
In the 1830's when McCormick's machine reaper hit the market two men could easily harvest 7-10 acres in a day. The invention therefore reduced the demand for hand labor in the North just as the cotton gin had done in the South a few decades earlier. Soon the North too began to soften their stance on slavery, albeit for selfish economic reasons.
I found it interesting that economics drove the slave debate much more than morals, from the founding of the country right up to the Civil War. Interesting too is how Northern and Southern states flip flopped on the issue along the way depending upon economic conditions.
