I'm under the impression there was a large sect of (mostly northern) framers that opposed legalizing slavery and discrimination laws, but compromised with the southerners for the sake of democracy. Did any of them acknowledge how this compromise will reflect them and their actions years down the road?
Right off the top of my head, I can only think of a quote by Thomas Jefferson, who said, "Slavery is like holding a wolf by the ears. You might not like it, but you dare not let go." This attributed quote was referenced in Ken Burns' Civil War documentary, which is why it is fresh in my mind. Since my Masters is in 19th century American history, this is a little outside my academic wheelhouse, so I'd be interested in what other Americanists with an 18th century specialization have to add! EDIT I realize this isn't exactly what you were asking about in terms of their legacy vis a vis slavery, but I think it does give a little insight into one particular Founding Father's notion that it was a problematic institution (to put it lightly).
As I recall John Adams' position on slavery was pretty vociferous near the end of his life when he and Jefferson had regular communication. More importantly there was a sense of concern about the legacy of the nation with slavery. Since I apparently have loaned out my two volume set of the Adams-Jefferson correspondence, which is where I would first go in order to find some of the quotes you might be interested in, I'll have to see if I can access it in another way or remember to whom I have given it. :)
One clarification: Are you wanting only to know what people thought during the time of the late colonial / early Republic years, or are sentiments such as Adams', even if later in his life, of interest to you?