Extraterrestrial civilizations. What is your opinion?

Well, if we're considering pathologies, then this is own same as an unplowed field for hypotheses :)
But still, there are exceptions, and there are rules that only confirm those very exceptions.

But in principle, if one approaches the problem scrupulously, the word "seen" should be understood not only as visually distinguishable, but also as experienced. That is, it's impossible to "see" what a person wants from you in a certain situation, but having similar relationship experience in the past, it's quite easy to figure it out. This is also knowledge of the seen, as it is based on real situations that happened to a person.
By the way, this also applies to aliens. Those people who have come into contact with them KNOW about their existence, although for everyone else these are all just theories and assumptions. Here, in my opinion, experienced knowledge prevails over simply "seen," because, I agree—with a good imagination, you can see anything :})