One of the things that make me skeptical that any UFOs are non-human or off-world in origin is their size. All UFOs, except perhaps in the most astonishing observer-specific experiences, are firmly stuck inside the scale of humans and their technology. This is epitomized in the classic image from the 1951 film The Day the Earth Stood Still:
While I don’t for a moment think that alien beings would be so anthropomorphic ... Read even more