Since the onset of my dementia/etc., one of the few things I've been able to focus on is UFOs--it's a subject I can come to and leave and it doesn't bother anyone if I don't make any progress; I was interested in it when I was young, and now that I'm old, why not look at it again. So, over the past few years, I read a lot of the early literature on the subject, and some of the more recent stuff. I'm trying to take a historical approach as much as possible, and have been constructing a detailed timeline...but that's for another time. Much of what I've read is nonsense, or at least does not contribute to understanding the phenomenon from a historical aspect, but one thing that bothers me is how both those who believe that there are sightings of unusual aerial phenomena and those who think there aren't any, BOTH seem to go immediately to INTERSTELLAR ALIENS as the theory to be accepted/dismissed.
'there are unusual phenomena observed' DOES NOT EQUAL 'aliens from space.'
There are other options available...
Personally, I'm more inclined to believe that there is some as yet unknown atmospheric phenomenon that has been largely ignored because it has been recognized to not provide much of a threat to people and technologies.
Past that, if one is to jump to unlikely, difficult to understand and undemonstrated solutions, I think the interdimensional traveler theory ought to be looked at. It has the advantage of not having to overcome the difficulties of interstellar travel, after all...