I think my favorite tell when it comes to the history of slavery and the founding is when someone says "almost no one thought slavery was wrong at that time." So, we shouldn't count the opinions of the 20% of the population that was enslaved in 1776?
It also lets off the hook the very significant number of white people in that era who thought slavery was wrong, but who out of concern for the economic interests of their slaveholding contemporaries agreed to go along to get along.
It also obscures the many people at the time who shared Thomas Jefferson's conviction that a) slavery was wrong but b) black people could not be freed and remain in the US because white people would never agree to live as equals with black people in the US.
Excerpts from TJ's Notes on the State of Virginia (1785) 
