If UFO's were a crime investigation, it would have been dismissed decades ago. If all accounts were consistent then it might be plausible. But it would be impossible for the myriad of UFO shapes, sizes, and contours would suggest that there isn't one Alien Civilization but many. Also I find it suspect that the technology and design of the UFOs seem to get more extreme as our understanding of design and mechanics advances.
We've gone from spoked wheels in the earliest accounts(The Spoke wheel was a new invention), to an Art Deco Disk design in 40's, triangular designs in the 60's and 70's as Jets became popular, Boomerang design in the wake of Stealth fighters, to now we've got Video of UFOs that looks like they were taken off the District 9 set.
While it's odd that the Zeno format of the extraterrestrials seem to stay constant.
Why would they come all this way to do nothing, seemingly for the most of us. But but probe hill Billies and mutilate cows for a select few that claim they have made contact?
Quest for resources is the only reason for any species to migrate. There doesn't seem to be a noticeable harvesting of any Earth's resources. Just a dashing friendly visit.
Also the time they seem to spend here, for a few fleeting seconds they can be seen cruising the sky, but then they dart off back into space.
With all of the different types of UFOs being reported, you would think one of them would be hostile and not waste time making it known. Considering the amount of time they spent to get here.
Most people who see UFOs don't report them out of a well founded avoidance of ridicule. I have seen two, and when you do see them, they are incredibly spooky and create primordial gut fear.
I saw one doing rapid right angle turns in the late dusk sky when I was a kid, weird and inexplicable, and later in adulthood a very visible and sizeable grey lozenge without wings, tail or lights quite low in the sky firing straight up the Napa valley in plain sight with no noise at all.
I don't spend my time looking for them, so if I saw them, they must be reasonably common.
If I had never seen them, I would never have believed the UFO stuff, either. The problem is, once you do see one, your thoughts about everything change inexorably. I do not blame the skeptics at all if they have never seen one.
IF aliens are here or are operating these things, they don't seem to need resources but conduct themselves with some kind of ethical hands off agenda or scientific curiosity.