They knew that they didn't possess clairvoyance and that they couldn't foresee what the future would bring. So they left the Constitution open-ended and made provisions for change. The very essence of the Constitution is that it charges the Federal government with promoting the general welfare at the direction of the people.

Sure. It was called the Amendment process, and some good (and not so good) things have come of it. It was designed to be difficult to do, and not something to be taken lightly.

Unfortunately, about ninety percent of what is considered "Constitutional" nowadays has been the opinions of the Supreme Court, which can look at a sentence like "Congress shall make no law" and decide it means something completely different.

How something like the income tax can be "unconstitutional" one year, and "consitutional" the next (what changed in the document in between?), shows that what is or is not constitutional has largely become a matter of who's running the court. It's not surprising that both political parties have a large interest in who gets appointed.

Geez, what's been done with the Commerce Clause alone...