Carl Sagan also said “Extraordinary claims require extraordinary evidence.”
He ‘believed’ in, and made a great argument for other civilizations existing.
But he didn’t prove it, and he accepted that. He wrote extensively about the logical fallacies that a lot of UFOlogists constantly used to ‘prove’ the existence of visitations.
The problem with UFO stuff is exactly as Astrothug says – you can’t really investigate it properly, because of the craziness involved.
A lot of the weird government coverups, crash scenes, etc, are now known to have been early stealth technology testing.
For example, the F-117 crashed all the time, didn’t show up on radar, didn’t look like any other aircraft, flew at weird angles, and when it crashed, the Air Force would show up, clean up the crash site, and deny everything, for obvious reasons. The F-19/F-117 stuff was totally secret stuff, and they didn’t want anybody even knowing it existed.
So a lot of times, when real scientists would investigate sightings and video evidence, they could rule out the usual explanations. But a lot of times they had no explanations. Now they do for a lot of the crash sites.
But to think that an advanced alien civilization (which undoubtedly exists), will take the time to travel to Earth and then mutilate cattle, create crop circles, and anally probe humans is just crazy talk. Unfortunately it’s this crazy talk that makes real UFO investigation impossible. As long as you give those things equal weight with the real unexplained stuff, then you’ll never be taken seriously.