Isn't that what democracies call "constitution"? Something that protects citizens' rights again wrong-doing of powerful entities including legislators and the state itself?
The people are "in power" just for that day while they're giving their blessing to their representative. After this, as long as things aren't too abrupt and disadvantage the regular person obviously enough to trigger a violent response, that representative can pretty much represent and defend any other point of view. Usually the one from the otherwise equal but not quite equal, much richer person. And with education being on the bottom of everyone's list, it just gets easier to cover these things up.
For things that concern interests far from home it's even easier. Freedom also means you're free to pump as much one sided information as possible. So as long as one can flood the people with Middle Eastern terrorism, Russian hackers, or Chinese human rights abuses, who's going to care about the home team doing the same even at home?
Superficially democracy is alive and well but it's like religion, most people observe it only in theory and when it matters to them personally. And when it does matter to them, it doesn't matter to enough other people. Which is why most talking points don't have a strong majority, and they're mostly dealt in a compromising way, which makes everyone equally unhappy (except a very few).
Thus the correct question to ask is "why/how did we break the system that used to work"
Following that rather than returning to a peacetime country and disbanding the associated military structure it was instead repurposed for a cold war in the face of another enemy that had sworn themselves to our complete and absolute destruction and which had the capability to do so. In the face of such constant risk of extinction almost any measure was seen acceptable to counteract the threat.
However after about 60 years the threat disappeared but the massive institutions built up to combat the threat then needed to continue to justify it's existence as careers and lives had been built upon counteracting the Red menance. Unfortunately these institutions did not cease to exist and continued the same tactics that it was profecient in despite the threat to the existence of the nation.
That's basically it in a nutshell.