As to why the aliens only contact nutcases, it could simply be that aliens actually contact a wide cross section of humanity, but only the nut cases are crazy enough to admit it.

Some thoughts on UFO encounters:

Someone once remarked, "The problem with UFOs is that they can look like about anything, while a black helicopter only looks like a black helicopter." This is a good guiding principle in cutting through a lot of nonsense.

One simple explanation for a lot of UFO encounters, that I don't see ever mentioned, is a drug smuggling operation. Yet, in reading newspaper reports of them, small planes will land in deserted areas, usually with their engines off. Picture some observer watching a mysterious light descending noiselessly from the sky in a deserted area. What are they going to think. They believe there is no place for a plane to land there and besides they would hear the engines, so it must be a UFO!

Someone stumbling on the operation would either be scared off or worse! One thing for sure is that the drug smugglers are not going to identify themselves as drug such! If the observer believes he's encountered a UFO and flees, so much the better!