I've always been of the opinion that if the government DOES happen to be holding aliens captive somewhere, it certainly isn't at Area 51. If anything, Area 51 is just misdirection.
More than likely, though, people are just batshiat insane.
A good majority of thinga are hidden in plain sight.
Not usually of that magnitude, however. You don't hide things in plain sight when you're trying to keep it secret from the other 99% of the world's population.