Too many flaws here to rebut, but if anything has changed over the past two centuries, it is the people, not the Constitution. There is nothing wrong with our governing document when individuals are capable of self-governance. You're placing blame on the wrong entity.
Well, that's just your opinion, man.
I might ask why you think the U.S. Constitution is so special when none of the Founding Fathers -- even the ones who supported its adoption -- thought of it as a magical document. For the most part, response was muted in the same way liberals and conservatives respond to Obama Care. Hamilton's camp thought they needed even more central power, Jefferson's thought they needed to stick closer to the original to the Articles. Everyone was pretty surly and pissed, but they needed something that would allow them to form a government that could face the imperial powers of Europe on equal diplomatic and military footing that they couldn't have as a confederacy.
Anyway, the people have changed because the world has changed. In a frontier society, opportunity -- the opportunity to improve one's self and one's condition -- is the direction of the frontier and is as far away as the next unincorporated territory. In the 21st century, opportunity is a leading export that most people don't have the economic standing to pursue and which wouldn't help them if they did. Gunpowder was the biggest threat, and it was a continent away -- the nearest threat was the sticks and stones of hostile Native Americans. These days, super plagues, nuclear bombs, rapidly dwindling resources and hunger for new territories, climate change, rogue states, and proliferating terrorism are the biggest threats, with missiles they can reach anywhere in the world in an hour. Responding to threats requires collectivization on a scale unimaginable to the Founding Fathers; a 1700s local militia might be able to guide people away from a flood or fight Native Americans, but it can't stop North Korea from pursuing nuclear technology.
As a last resort, anyone in the 1700s could avoid starvation and supplement their diet by hunting and trapping, a feat reduced mostly to recreation in a society where populations are tens of thousands of times bigger and only factory farming on a super massive industrial scale can provide humans with enough food to remain fed. Aka, self-reliance is hopeless on a fundamental level; if everyone
had to be self reliant, tens or hundreds of millions of people would have to die because nature wasn't supplying enough livestock to keep them fed no matter how skillful of hunters they were.
Nobody has a time to multi-task into self-reliance, anyway, because our economic order requires each individual to invest every ounce of their time into learning a specialized skill, like driving a huge truck across Alaska, accounting, or soldiering. There isn't enough time to learn
all the skills you need to maintain the technological complexity of a modern home.
Don't know how you expected anyone to stay the same as we were two hundred and fifty years ago when everything is so different.
