It was, of course, merely Asimov's opinion that “if the aliens are there, then they should come down and say hello, or go away and leave us be”. Why aliens should take any notice of what he thinks is an interesting question.
Not sure I agree with you that it is “a capital mistake to theorise before one has all the data”. Unadvisable perhaps, and one should not be dogmatic, but there's no reason not to form tentative hypotheses while one is collecting more data.
“What we actually know about UFOs could, as my grandfather used to say, be written on the back of a postage stamp with room left over for the Lords' Prayer”. Not sure I agree with you there. You go on to say that there are “a significant number of unexplained ones”. Agreed “we do not know [for sure] what these phenomena are”. Nevertheless, as I argued, aliens seems the simpler explanation, as compared with secret human programmes.
If “many of the ideas presented by UFO apologists violate common sense”, then we should focus on the ones that don't. And of course, common sense does not always come up with the right answers. It's a rather subjective guideline, depending on your preconceptions.
Don't agree with you about the Ancient Alien material. You say that “it's already been shown that humans had the capacity to build all those monuments with what they had to hand”. I would say that skeptical debunkers, who are prejudiced against the alien suggestion in advance, have attempted to demonstrate this. But I would say that they have not taken all the data into account. And if the data is inconvenient, they deny it. The other problem is that you have to agree with what the ancients “had to hand”. Sceptics would argue that the Egyptians didn't have technologically advanced drills when they built the the Great Pyramid. Yet this was obvious to the engineer Christopher Dunn when he inspected the site. That's not evidence of aliens, of course, merely that the Egyptians were themselves technologically sophisticated.
And what do think the ancients had to hand to put 800 ton-stone blocks precisely into place?
Not sure I agree with you about Project Blue Book. Nor I'm guessing would Hynek. Have you read his books? You're right about the motivation for keeping such things secret. Public reaction might be panic.
“It's becoming increasingly impossible for governments to hide anything”. That's presumably why the US government is being forced into some kind of declaration in June [hopefully].
