My friend, the invention of the cotton gin did just the opposite of what you claim. Before the gin, the only cotton that could be profitably grown was the long fiber or 'low-land' variety. It was not a major crop because it was very geographically limited.
With the gin, the short fiber or 'upland' variety could be profitably grown spreading cotton production all the way from Georgia to Texas and as far north as Missouri and Tennessee. It infinitely increased the demand for slaves to plow, plant, how and pick cotton and the price of slaves sky rocked to the point that in 1860, slaves were the most valuable property in the nation -- more valuable than all the railroads and factories in the notion combined.
With the gin, the short fiber or 'upland' variety could be profitably grown spreading cotton production all the way from Georgia to Texas and as far north as Missouri and Tennessee. It infinitely increased the demand for slaves to plow, plant, how and pick cotton and the price of slaves sky rocked to the point that in 1860, slaves were the most valuable property in the nation -- more valuable than all the railroads and factories in the notion combined.
Excellent post. Without the cotton gin history would have been very different. Slavery wouldn't have been as firmly rooted. Slaveowners wouldn't have been quite so well-off and confident about their institution. Slavery might not have appeared so essential and beneficial to so many people.
You can see some of the same kind of wishful thinking in Jefferson's own assumptions. He came to believe that spreading slavery territorially would make it easier to abolish the institution. Or at least he said that. But of course it didn't work that way.