Yes, it is adaptable, but it was also based on certain immutable principles ("We hold these truths to be self-evident... ") that form the basis of free civil society, as well as the idea of the social contract ("That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it"). It was also structured with the idea that power should be limited, diffused, and separated among the various branches of government, with each branch serving as a check against the others. These principles have served us well, and until someone gives me a good reason to change them I think we should keep them.
The FF meant to say "All white men who own property are created equal." They were not inclusive of minorities, women, indentured servants, gays, or indigenous peoples.
Nevertheless, they envisioned the possibility that their worldview might need to be updated at some point, so they created a mechanism (constitutional amendment) by which to accomplish that. While conservative white men fought tooth and nail to maintain the status quo, Americans used that mechanism to free the slaves, allow women and native Americans to vote, and require all the individual states to adhere to the rights embodied in the Bill of Rights.
Nevertheless, there have been those who railed against allowing minorities, women, gays, and others from reaping the full benefits of citizenship. Even in this modern era, there are those who inexplicably opine that America was better when slavery was allowed to exist. They extol the virtues of the men who waged a Civil War against the United States in order to preserve their economic system, which relied on slave labor.
Since slavery as it was in the 19th century is now unacceptable by most modern civilizations, conservatives now enslave the masses with sub-poverty wages and say "It is fair," all the while corporations reap the largest profits in human history. They seek to deny basic life necessities to millions, like access to affordable healthcare, clean water and clean air, while making sure the masses bear the greatest burden of taxation. They tell us "corporations are people" and therefore corporations must enjoy the blessings of "free speech" and they tell us that money is the equivalent of speech. Therefore, corporations, millionaires and billionaires must be allowed to spend their free speech on political elections at every level. The end result is the 1% have the best government money can buy and the rest of us can kiss their asses.
And the really sad part? There is a large portion of our population who are convinced that the millionaires and billionaires are looking out for them, that the 1% are the guardians of democracy, champions of the masses, the working class, the impoverished, and the disenfranchised. They cheer as their sons and daughters are sent away to fight and die to advance the financial interests of those 1%. And then they try to understand why their lives are so burdened. They look to blame someone for their lot, and they are told, "It's the peasant coming across the border who is your enemy. It's those poor brown people who are making your lives so difficult." It has always been so. Today it is the Mexican immigrant who endures the brunt, years ago it was the Italians, the Puerto Ricans, the Irish, the Jews, the Chinese. Some things never change.
