Condemning 18th century people because they didn't live their lives by 21st century cultural norms is a silly argument. Plenty of our philosophical and political concepts come from ideas as old as the Greeks. We don't reject valid ideas because the society that produced them didn't live by our modern values. Of course they didn't, they were a different society.
We can't agree with each other in how we should behave NOW, but we should condemn people from the past because they refused to live by proper modern standards, too?
You think you are so much more enlightened than the past? Guess what? So did they. Every generation, no matter how far back you go, thinks they were the most modern, most enlightened generation in history. And yet a few generations down the road, and they all start to look old- fashioned.
When the Founding Fathers wrote those documents, NOBODY had created a nation based on the concepts and standards that became the American government. Every other government in the world favored the wealthy and well-connected. America would be the first nation where the lowliest citizen still held the exact same rights as the wealthiest.
We haven't always lived up to that promise, but that promise still remains, and it is still a worthy promise to defend. I hear people celebrating the death of America, without any consideration about what would replace it. Nobody has suggested a better system, and destroying the current system, with nothing to replace it, is ALWAYS a bad idea.