The simple fact of the matter is that the public doesn’t really know much about what goes on at the military base near Groom Dry Lake, Nevada (popularly but not officially called Area 51). It is a top secret military base, and there are of course perfectly legitimate government and military reasons for keeping the base’s purposes secret that have nothing to do with aliens or UFOs; 60 Minutes correspondent Leslie Stahl suggested that the area may be a dumping ground for toxic waste. There’s no reason to think that anything alien is going on there, but where there is secrecy, there will be conspiracy.

Further reading:

Robert Carroll. The Skeptic’s Dictionary. Available at http://www.skepdic.com/area51.html.