I continue to be amazed by the insistence on judging the Founders, and/or other historical figures, by modern standards.
People are born into the society they are born in; they grow up with certain things as norms. It is the rare person who rises above that at all; to hammer them because they didn't rise quite far enough to suit our modern sensibilities is a bit ridiculous.
Future generations may judge us as harshly, deciding that by their standards, we were a bunch of hateful barbarians.
You have to judge historical figures within the context of the society they lived in. IMO when you do so, the Founders come out as being well ahead of their times... just not quite AS far ahead of their times as some might wish, who wish to use that against them.
The slavery compromise was forced on them by the slaveholding states as the only way to preserve the nation as a union; they still feared Britain enough to accept the need to keep things together. Anyone recall the War of 1812? Occurred to anyone that they might have put unity against the ongoing threat of Brit/European attempts at reconquest as a high enough priority that they let the slavery issue "ride for the time being"?