Jacques Vallee, a noted computer scientist in his own right, is one of the best reads if you're interested in this stuff. He's not a crackpot and doesn't seem to be pushing an agenda one way or another.
"Vallée proposes that there is a genuine UFO phenomenon, partly associated with a form of non-human consciousness that manipulates space and time. The phenomenon has been active throughout human history, and seems to masquerade in various forms to different cultures. In his opinion, the intelligence behind the phenomenon attempts social manipulation by using deception on the humans with whom they interact."
To wit, there seems to be an intelligent phenomenon going on, and it appears throughout history. He doesn't say anything about what it could be, simply is describing the phenomenon.
Also, I've read his books. Wikipedia quotes don't really give the same impression as his writing.
It appears to have an observer quality to it. The one that sticks out the most in my recent memory is the 2006 Chicago O'Hare sighting. I remember this going through a pretty quick 1 or 2 day news cycle. Fairly alarming given the number of people witnessing the phenomenon and the backgrounds of the people observing it.
Obviously rainbows are an example of a shared hallucination and the phenomena manifests differently dependent on the observer's viewing angle. At the moment I'm not convinced these aren't unexplained atmospheric phenomena because I've never seen one. I know some ideas put forth include ball lightning for at least some UFOs. Assuming these cases to involve intelligence may just be our misinterpretation of the phenomena.
It’s refracted light arcing in the atmosphere. That’s not a hallucination. Treating it as some continuous entity is a hallucination of our minds. There’s nothing suggesting the start of the arc has anything to do with the end, but we call the collective refraction phenomena we witness a rainbow. UFOs could also be something that we collectively fail to comprehend well enough to categorize the constituent parts.
The majority of people throughout all history have believed in the supernatural. If you're one of them then this is probably the best explanation for the UFO phenomena. None of the naturalistic explanations are 100% satisfying.
As a sidenote I've noticed a lot of people in the UFO/ET community no longer believe ETs are from another planet. Most seem to think they're "interdimensional" beings (which just sounds to me like sciencey way of saying supernatural).
