The Constitution says what now?

It is a source of constant amazement to me the way literate people who have ample ability to read the U.S. constitution seem to have no idea what it says. In fact it seems that few or perhaps none of the people occupying positions in any of the three branches of our government have ever read our founding documents. People, politicians, and Supreme Court justices alike reinterpret the Constitution and Bill of Rights in such ways as to drastically change the intended meaning of the original words. Other times phrases and clauses are attributed to the Constitution that are simply not there. The most common one that comes to mind being the oft cited 'seperation of church and state' which an alarmingly large number of people seem to think is something our founders put into the Constitution to save citizens from ever having to see or hear anything the least bit faith related anywhere other than inside a place of worship. Our founders knew what they were doing when establishing the structure of their new nation. Their writings as well as the Constitution and Bill of Rights themselves make clear the founders intent and the rules by which the United States is to be goverened. Why is it that as a nation our knowledge of our own constitutional rights is so poor that, as we are losing them one by one, we are oblivious to it?