Progress, far from consisting in change, depends on retentiveness. When change is absolute there remains no being to improve and no direction is set for possible improvement: and when experience is not retained, as among savages, infancy is perpetual. Those who cannot remember the past are condemned to repeat it.

- George Santayana

That's the full quote that people like to reduce to the final sentence.

Documents are a species' way of remembering the past and establishing core ideals so that future generations don't have to reinvent those wheels.

Not to say any given document is without flaws or captures the right values, and as our societies grow and mature so too should the values that we align ourselves with.

Well you benefit from that very same document right here (free speech). The first thing tyrants do is get rid of things like constitutions.

Idolizing a document over human rights is terrible.

Well, to be clear, human rights, other than being a vague philosophical concept, are also a document. Much younger, and much more sensible and uncompromising, but still also a document.

Hopefully if new rights are deemed to be needed, they can be added.