Well, let's give some reasons.
Most of the generation that has this belief was raised during the cold war and were told, "Your government is here to protect you from the Russians and Communism."
The other generation has never had anything like that, sure there's terrorism, but that's something different than the big bad Russians.
Terrorism can't launch missiles at you when something doesn't go there way, at least not in The States, not yet.
During the Cold War Americans were told their government was the good guy, that they were doing things to help them, not to harm them and they went along with it.
The Generation of the Cold War listens and obeys its government because, it's been told that so many times that it believes that whatever it does is for the good of the people, but what if that's not true anymore?
Two Generations
The CWG (Cold War Generation)
The CWG (Cold War Generation) loves it because it was told the Russians has missiles aimed at it and that any moment they would be obliterated in a flash of light, I've heard this statement from CWG's.
The PCWG (Post-Cold War Generation) has heard the stories from relatives about the Cuban Missile Crisis and living in fear of being annihilated at any moment, but they never lived through that, sure 9/11 made them think about it, but to compare 9/11 to the Cold War is off base.
9/11 was something that we couldn't plan for--unless you believe the conspiracy theorists--it was an event that changed the country, and it could have been for the good, but it wasn't, this where the PCWG comes in.
The PCWG
Though they may share their beliefs, they are finding themselves troubled by recent revelations about the governments activities, namely the leaks from Bradley Manning and Edward Snowden.
The two things changed the beliefs of this group, they most likely have seen first hand what the government has done, either through the bailout of the banks, the handouts to Big Oil, Big Pharma and Agri-Business.
They've seen the country in dark nights--9/11--and wonderful mornings--DOMAStruck Down. They are more likely not to care about ethnicity, sexual orientation or religion.
They want their government to help them, not to control what they can and can't do.
For PCWG they've heard how great their government is, but all they've seen is wars, poor, loss of jobs, handouts to banks and a Legislative and Executive branch of government that care only for its own interests and not those of the people they represent. They've never seen this wonderful government their parents, grandparents or others have told them about.
They've never felt their government was helping, only hurting their citizens.