Except that it wasn't poorly worded or ambiguous when it was written; it merely seems that way to people who don't understand linguistic drift and are not scholars of history, and that view is encouraged by those who use said ignorance to distort the original meaning in order to push their own agenda -- something both advocates and opponents are equally guilty of.
That said, the Constitution was designed in such a way that it could be updated as needed to meet the needs and principles of a changing culture, along with safeguards to help ensure such changes were not made whimsically or without a great deal of popular support. It's not a perfect system, but no human system can ever be perfect.
IIRC it was also supposed to be exposed to study and possible revision regularly............