Epic Rap Battles of History just did a contest between Thomas Jefferson and Frederick Douglass, and by far and away the most stinging line was when Douglass said to Jefferson “You let freedom ring, but never answered the call” in reference to Jefferson writing against slavery, but still owning slaves.
I think if the American Revolution had been just ten years delayed, slavery may have been outlawed, or at least severely restricted, at the creation of the Constitution. Most of the Founding Fathers were very much against slavery and even those who participated in it, like Jefferson and Franklin, would not have objected to the abolition of the slave trade.
It is a “hideous blot” on our history (the words of Jefferson) and we must acknowledge it. But that doesn’t mean that anyone alive today should be held accountable for the situation a quarter of a millennium ago.