1) The NSA doesn't have oversight; they're a black operation, part of the black budget, and they're basically accountable to know one. The Snowden leaks prove that. The NSA can access almost any of your communications anytime, anywhere they want. How do they keep people from blabbing? Well, I don't know your background (I stick to the Neaderthal Haven mostly, so pardon here), but if you've ever done an SF-86 for a TS clearance, then actually read the NDA you have to sign, you know it's better to shut up and not risk it. There's a reason Snowden is in Russia and will stay in a non-extradition treaty country until his death; breaking that NDA is basically viewed upon as treason, which is punishable by death. Ever noticed you don't see many people leaking state secrets, and when they do, they go directly to jail, do not pass go, and do not collect $200? The TS NDA covers that. Long story short: what you see cannot be repeated under any circumstances. You are to die with this information and for this information. Release of this information is punishable by termination, jail, and any applicable sentence thereof. There's also the small case that some of the people honestly believe in the mission.
While sitting in the SF airport and Portland airports, I saw bags getting left behind multiple times. I glanced around to see if anyone else noticed; guess what? Most people had their nose stuck in a cell phone not caring. I've seen the same in train stations and metro stations here in DC (it's one of the myriad of reasons I hate riding transit out here).
The thing is, terrorists don't care if they get caught; that's the whole idea: instill fear. Whether they bomb something or not, their mission has been accomplished. Once fear is instilled, all is right for them.
Personally, as a US citizen, it is my responsibility to be on watch for suspicious people acting oddly, not the government's. Maybe it's because I work with the government and I realize they could screw up their own erotic dreams, but I wouldn't trust the government to sit on their butts and collect a paycheck without screwing it up (as evidenced by several porn-browsing-during-work-while-the-country-crumbles stories).