Just a thought I had today:
The closest star to our planet is 4.2 light years away. Let’s assume life exists there, and they have ships advanced enough to fly ten times the speed of light. That means it would still take them over five months to get here. Even for a four-man (-being?) crew, you’re looking at stocking lots of food and water (or equivalent sustenance) for such a long trip, meaning the ship is going to need a sizable cargo hold (whether for stored goods or a garden). Then you need more space for propulsion unit.
This rules out the small UFOs most people claim to see as alien in nature. If they traveled through wormholes or jump gates, folded space, or traveled via some other sci-fi cliche, how is it we can spot the energy signatures of gamma-ray bursts in remote galaxies, but not something local to our solar system?
Not to mention the time and energy investment involved. They’re going to come all that way to buzz an airfield, make crop circles, probe a redneck, and fly home?
Yeah. Still not buying it.