I've argued this for a long time and ruffled plenty of feathers doing it.
I have no doubt that the observable universe is teeming with life, but I doubt it is intelligent tool-using/space-faring life. If this turns out to be
true, where does that leave existing UFO reports and eyewitness accounts? I'm going to start with the most obvious reasons for UFOs (and most
controversial) and work down from there*:
1) Misidentified natural terrestrial phenomena.
2) Misidentified (and largely "unknown" man-made terrestrial phenomena.
3) Liars, charlatans and attention seekers.
4) Mental illness.
As for close encounters with ETs (and "alien" abduction):
1) Victims of a man-made hoax perpetrated by one or more groups/powers.
2) Liars, charlatans and attention seekers.
3) Mental illness.
*Caveat: the psychodynamic "solution" remains remains an open question. In other words, there is a phenomenon, be it natural, psychological,
metaphysical or spiritual in nature, that has been a part of human nature/existence for many thousands of years. This phenomenon is reflective of our
current technology and tends to mirror our own deep-rooted "fears" concerning our social/psychological/technological advancement. The Romans saw
"flying shields," the renaissance Europeans saw "flying chariots and crosses," the Victorians saw Leprechauns and "airships," and the post
second world war west saw nuts and bolts spaceships (who were/are obsessed with our nuclear technology).
This phenomenon may be a manifestation of our collective id or "leak" through from another dimension (that we have no current way to identify,
measure or image in any meaningful way).
But it's probably not a spacefaring ET, because the chances of those existing per the Fermi Paradox/Drake Equation is vanishingly slim.
Side note: I don't believe we should slow or halt our exploration of space, via radio, infrared or any other form of telescope. I *do* believe the
universe is literally "ours" for the taking/up-for-grabs and that we have a moral/psychological/physical imperative to survive, thrive and claim it,
and I believe we can do so in about ten million years (which is nothing compared to the life of the universe) and that we can do it without warp
drives, space "folds" or other forms of FTL wizardry.