There are so many wild conspiracy theories flying around the world, if one was to believe 10% of them one could hardly dare to go outside. When it comes to this Area 51 thing - I can't see how any of the conspiracy theories surrounding that have been confirmed? An idea that it was, or is, a place where the USAF tests experimental aircraft is hardly a conspiracy theory in the first place.
And this PRISM/NSA story? Wow, an intelligence organization in the world's most powerful country carries out surveillance of internet activity that they find suspicious? The news is that it was leaked. Do anyone believe that China and Russia don't do something similar? Not that it makes it morally right, but I'm not very surprised.
The step from that, to "the US government staged 9/11" or "freemasons control the world and have done so for 200 years", is long.