On so important a question as UFOs, the evidence must be airtight. The more we want it to be true, the more careful we have to be. No witness's say-so is good enough. People make mistakes. People play practical jokes.
People stretch the truth for money, attention or fame.
People occasionally misunderstand what they're seeing. People sometimes even see things that aren't there. The whole idea of a democratic application of skepticism is that everyone should have the essential tools to effectively and constructively evaluate claims to knowledge. All science asks is to employ the same levels of skepticism we use in buying a used car or in judging the quality of analgesics or beer from their TV commercials. But the tools of skepticism are generally unavailable to the citizens of our society.