After all, in those 30 years since UFOs appeared, modern science has undergone several generations of radical revolutions in its comprehension of the Universe, from the cosmic and macroscopic to the microscopic and subatomic scales. The inability of ufological theorists to come to grips with these objections represents the most serious roadblock to the acceptance of ufology as a legitimate branch of modern science. Ufologists assert the existence of some extraordinary stimulus behind a small fraction of the tens of thousands of UFO reports on file. UFOs is that it is impossible for science ever to prove a universal negative. There will always be cases which remain unexplained because of lack of data, lack of repeatability, false reporting, wishful thinking, deluded observers, rumors, lies, and fraud.
Unexplained cases are simply unexplained.
They can never constitute evidence for any hypothesis. It is not necessary to conjure up visions of blind, drunk and dishonest UFO percipients to cast doubt on UFO reports. The vast majority of UFO witnesses apparently are honest, sober and intelligent people faced with an extraordinary perception. Yet there are amazingly many obvious and subtle ways in which such perceptions can be understandably generated. And there is bound to be an artificial residue of unexplained cases, a residue created purely by bizarre coincidences, by limitations on human perception and memory, or by rare undocumented natural occurrences.