Too often the founding fathers are worshiped as near perfect men who had the best ideas that will always stand the test of time. Not only is this incorrect, it's very harmful to the progress of our country. The kicker is, I think they were smart enough to recognize that.
The founding fathers were rich, white, land owning men that were in a much different economic, social, political, and military time than we are now. They got together to found a country that was largely built around protecting their interests as wealthy land holders while also providing for more freedom from the oppressive monarchy of England. This resulted in a Constitution that is meant to protect the liberties of all people, well, all people that were rich, white, land owners. As we look back and examine the ideas of figures such as Thomas Jefferson, George Washington, and James Madison we see they had some phenomenal ideas! Ideas that were unprecedented! However, they also had some ideas that many would consider anathema to America today. Slavery, Women's Suffrage, Native American lands, taxation and many other ideas we find repulsive. This doesn't mean the founding fathers were evil men bent on making life horrible. It means that the founding fathers were a product of their time and economic status.
It is key to remember to put the past into perspective when advocating the Constitution. It is a living document and was designed to be so, and the founding fathers were far from perfect.