Disclaimer: I love the entire "aliens" mythology, and although I remain very very skeptical, I have seen many strange things down here in the skies near NASA. I also live a few miles from Patrick AFB, and they run training in C-130's directly over my house from time to time.
Regarding "Area 51": I have followed this story since 1992, when I discovered it via an episode of the old show "Sightings" on FOX as a 12-year-old boy.
If I remember correctly, Bob Lazar, who has been confirmed as a fraud, contacted a local journalist with the story. The story went national, and the entire Area 51 story became a mecca of conspiracy theory ever since.
Most of the non-woo theories discuss technology used to monitor Soviet technologies, specifically their aerospace and nuclear capacity. I'm sure we've all seen the famous newspaper cover with the headline "Flying Saucer Crashes in New Mexico", which was later recanted and explained to be the debris of a weather balloon.
Many have speculated that rather than a weather balloon, "they" were testing spy balloons, and that once the remains of one of these balloons had been found, they were forced to invent a "cover up" story so that their covert operation against the USSR could continue.
Other speculate that the Roswell crash was an experimental high-altitude spy plane. Perhaps a beta version of something like the U-2. Others claim the U-2 was old hat by the 1940's (I doubt this very very much) and that the crash was a prototype of the B2 (which I must admit, looks a lot like how I would image an alien spaceship to look).
The problem with both of these speculations is the timeline. The Roswell crash took place on July 7, 1947. The U-2 was a project under Eisenhower, and wasn't revealed to the public until the soviets captured one in 1960. McDouglas Arthur and Northrop Grumman were both experimenting with the "fixed wing" design in the early 60's and 70's, but the B2 (aka Stealth Bomber) wasn't ready until the early 80's, and only revealed to the public in 1988.
Some claim that "they" have technology 20-30 years ahead of what they released, and that its quite possible "they" were testing a prototype B2 in 1947; 40 years before this plane would be revealed to the public. My question to these people is: what did the Government do with these "beta" B2's for 40 years? And assuming that they didn't do anything with them, in order to keep them secret, what was the point of having them? The "they are always 20 years ahead" mantra fails the "sniff test" IMO.
However, I have a conspiracy theory of my own regarding Area 51. I think the government invented a story about crashing UFOs, made up a few puppets, and then slowly "leaked" this information to a few people with questionable credibility.
Why would "they" do this? To cover-up spy balloons and experimental jets from the USSR? Possibly. But I have an even more rational excuse: to cover-up toxic waste.
Note: I really wish I could post a link here, but a little Googling will quickly confirm this.
In the early 1990's, a group of employees who had operated out of Area 51 began getting very sick. After a few died, the survivors banded together, and began asking what had been at Area 51 that was making them all sick. Naturally, the government claimed "it was a secret in the interests of national security" which fueled the alien story into overdrive. Remember: it is my theory that the government itself was the original creator of said legend. But why?
When all was said and done, after several changes in venue, countless appeals, and several more deaths, the case proceeded to trial where it was discovered that Area 51 had been used to store toxic nuclear wastes. This toxic waste had been buried in the desert, and now, 50 years later, had cause some serious health effects to the people. You can imagine how this ends: a big fat settlement for the victims, and a nice splat of egg on the government's face.
So my theory has always been that the real secret of Area 51 was toxic waste. "They" knew they had a health risk, and "they" knew the public would scream and yell if this became public information. How do you keep people from discovering the truth? Distract them with something more interesting.
Such is my theory. Sources: none. Credibility: none. Basis: too much thinking. Take it with a grain of salt.
However, you gotta admit- if you didn't know what a B@ was, and it flew over your house, you would assume it to be a UFO.
Also, I see weird stuff in the sky all the time. Are they NASA/AF experiments? Alien visitors? Sleep deprivation? If Occam's razor is any guide, probably the former, or the latter.
And it goes without saying that if aliens wanted to be known to us, they would be. They would land on the white house lawn during a scheduled press conference. So if the aliens *do* exist, and the government *does* know about it, you have a bona-fide intergalatic conspiracy here. Congratulations. David Icke would be proud.