Again. What I'm seeing is confusion between what UFOs are defined as for the sake of inquiry and what the actual objects described in UFO reports are. When these two concepts are separated,1) there are plenty of facts upon which to support the definition of UFOs as alien craft. Those facts are based on the content of UFO reports that describe what appear to be such craft, how the official definitions were formulated, and how people in general have interpreted what the word means from its inception all the way up to the present.
What exactly the objects in UFO reports really are and where exactly they're from is another matter. However it is entirely reasonable that if a number of people observe something, the characteristics of which appear to be that of a craft that is strange and seemingly out of this world, and that after investigation by independent specialists, nobody, including USAF officers with Top Secret clearance can identify the craft as being part of any military or civilian project, then it is entirely fair and logical, based on the content of such reports, to consider that if such reports are accurate and true, that what is being reported is actually some sort of alien craft.
That doesn't mean that there aren't other strange phenomena reported in the sky from time to time, like giant birds, Earth lights, ball lightning, and whatever else we might see besides UFOs, and indeed, it would be a complete mistake to classify those as UFOs because not all strange phenomena seen in the sky look like alien craft, and that is exactly the point I've been trying to make. So maybe we're actually in complete agreement on the fundamental point, but just coming at it from a different angle.
Now with respect to the ETH, I don't claim that it is a certainty that UFOs are ET. I do claim that they are alien, and by alien, I mean it pretty much as it is defined in the English language, which strongly implies that they could be ET, which IMO is perfectly fair, but also includes other possibilities, e.g. "strange: outside somebody’s normal or previous experience and seeming strange and sometimes threatening" - Encarta, or even more specifically, as analogous to its usage in biology where it means, a species that's non-native to the environment or body in which it is found.
In this case 2) UFOs appear to be non-native to the body of human civilization that the vast majority of us are familiar with. So perhaps they might come from some remote unexplored place in the depths of the ocean, or are part of some secret society. I don't know, but either way, the word "alien" still covers that with respect to the subject matter, whereas ET doesn't, which is exactly why I prefer to use the term "alien" rather than "ET". Personally, I do think that the ETH is the most logical candidate, and that the originating location is probably someplace within 100 Light Years. However exotic ET possibilities. like worlds in other universes might also be the case, though that is much more of a stretch.