Deciding that slavery was wrong was much easier than deciding what to do with millions of people from another continent, of another race, and without any historical preparation for living as free citizens in a society like that of the United States, where they were 20 percent of the total population.
It is clear from the private correspondence of Washington, Jefferson, and many others that their moral rejection of slavery was unambiguous, but the practical question of what to do now had them baffled. That would remain so for more than half a century.
In 1862, a ship carrying slaves from Africa to America, in violation of a ban on the international slave trade, was captured. The crew were imprisoned and the captain was hanged in the United States -- despite the fact that slavery itself was still legal in both Africa and the U.S. at the time.
What does this tell us? That enslaving people was considered an abomination but what to do with millions of people who were already enslaved was not equally clear.
That question was finally answered by a war in which one life was lost for every six people freed. Maybe that was the only answer. But don't pretend today that it was an easy answer -- or that those who grappled with the dilemma in the 18th century were some special villains, when most leaders and most people around the world at that time saw nothing wrong with slavery.
Incidentally, the September issue of National Geographic had an article about the millions of people enslaved around the world right now. But where is the moral indignation about that?