Prefacing this that I am not an American, hold different values to most Americans and do not study philosophy, sociology, history, politics or education. So this is merely my outside opinion... Also of note this is only tangentially related to the topic currently being discussed so feel free to ignore me. Anyway let's get to this:
As for instilling greater respect for democracy and civics, I doubt a more nuanced view of history would do so. Looking at history from a less simplified perspective, we're reminded time and time again that, for instance, the Founders intended to create an aristocratic government, one that was and continues to be dominated by a wealthy elite (fun fact: even white males did not have the right to vote in many states). And when democracy actually became viewed as a good thing, our nation began doing everything from committing genocide to enslaving blacks to propping up dictators, all in the name of an intangible, unachieved "democracy." When people are confronted with this harsh reality, it's very possible that they lose respect for the government that they were once taught is ideal and perfect, rather than gain respect for it.
I believe this is correct, but that the problem isn't with looking at modern history (what an odd phrase) but the idealisation of the early history and historical figures of your country...
We still celebrate democracy here (literally on Guy Fawkes night) and uphold it's values; without idealising it or its instigators. British democracy has its roots in the magna carta from 1215, but it's common knowledge that the events surrounding it's creation were dubious at best. In the real world there are no great people, not really, we are all flawed human beings and upholding people as some kind of pinnacle can lead to many problems... Especially if those people are a bunch of dead oligarchs from over 200 years ago.
The world continues to accomplish many things and has over the millennia, viewing any one part of history as some kind of golden age leads you to view everything else with distortion...
People learning about the past, about history and society, I don't believe they should be told what is right and what is wrong; debate can be had about whether or not past events are right by modern standards, but the idea of enforcing those modern standards onto the learning process irks me greatly. We currently view democracy and democratic systems as the best, most right system, but how can we ever improve and change them if we hold onto the past so strongly, and teach the thinkers of the future that it's the only correct way.
Focusing in on Tau's last scentence
"When people are confronted with this harsh reality, it's very possible that they lose respect for the government that they were once taught is ideal and perfect, rather than gain respect for it."
The problem is that they were taught it was ideal and perfect, nothing is perfect, perfection is as much a fairy tale as Santa Claus, it's an unachievable, impossible goal. And distorting anyone's view of anything to be perfect is inherently flawed.