I would use my own words, but daveschoder summed it up so well over in this comment at SlashDot:
We can't keep any of our classified programs secret; we have people coming out of the woodwork at AT&T and within the intelligence agencies themselves to leak every possible program we've got going on in the "war on terror", but yet we can manage to keep it secret that the government itself directly planned and executed 9/11 and also murdered 3000 of its own citizens, despite millions of pages of evidence to the contrary, Islamic extremist organizations the world over, and so on - this is getting better than Holocaust denial!
Like I've told Number 1 Son: Nixon and the plumbers couldn't keep a simple break-in secret. I used to suspect that the mafia had killed Oswald, but even the mafia couldn't keep that kind of secret. No, there's no way 200+ people have kept the Aliens secret at Area 51, or that Dub and crew fixed the WTC buildings, etc.