Don't you think that hackers would've revealed that it's possible to activate the camera on a MacBook without turning on the green LED? Unless you believe in some sort of conspiration that would've "silenced" every hacker who discovered this security hole, which in my opinion would cross the "paranoid" line.
We cannot know what happens to data we send over the internet or whether our phone calls are intercepted by some organisation. But on actual devices, it's possible to know when things like the mic or camera are used and observe the data which is sent outside, and you can bet that some "paranoid" hackers are looking for this kind of unauthorized data collection all the time.
Don't download ANY app released by the NSA. But it wouldn't surprise if they can already activate your camera and mic. I doubt turning off the little green light is beyond their capability.