So you pick the much more likely scenario: aliens. "Citizen, the aliens are coming! Let us 'protect' you...." Silly cattle.
No, I never "picked" that one. I simply find it not impossible, for all the reasons I described on page 3.
I find the unknown types of complex, long-lived ball lightning to be quite a likely scenario for many of the remaining unknown cases. Possibly, such things could create a radar signature, would "follow" aircraft, and would appear to be spheres, saucers etc. generating bright light(s). They might even appear to have metallic bodies. However, there are a few other accounts which seem to indicate things that would be very unlikely for ball lightning to do.
Let's look at where we are here:
IF M-E effect, or something like it (Heim theory seems fully debunked now, but it's another example), works, THEN it might be possible to engineer a (sublight) gravinertial space drive.
IF you can manipulate gravity and inertia, MAYBE you can generate negative energy densities/negative mass.
IF you can generate negative energy density, MAYBE you can manipulate it to form something like a bubble, in which case you may be able to generate something like an Alcubierre metric (superluminal space drive).
If that's so, then interstellar flight, while still non-trivial, would not be as big a deal as we think it is. So, you might once every few years send a recon force to swing by a planet with an emerging civilization and conduct observations for a few weeks to see what direction they're headed in. Better to be prepared for a new player on the scene.
So, that's why I find UFOs not impossible. My reasoning isn't too far from GIThruster's, the main differences being:
1. He seems relatively convinced that M-E, negative energy, and Alcubierre metrics or wormholes CAN be generated
2. He seems to heavily favour the UFOs are aliens explanation
3. Given that he apparently strongly suspects that points 1 and 2 are real, he draws a causal connection between the two: UFOs are using M-E devices to create warp drives and so are routinely coming here.
4. He also seems to think that at least the U.S. government (maybe other governments) knows that this is what's happening and is deliberately covering it up, for which I not only find no evidence, but also find unbelievable based on what we know of bureaucratic politics/behavior.
Now, you may find it more believable that there is a fleet of secret U.S. government advanced science craft flying all over the earth, which is fine. Admittedly both aliens and a secret U.S. program which has successfully stayed hidden for decades while we waste money building jets and rockets both seem bizarre, but are both marginally within the realm of the possible. So, I suppose that, based on our own personalities, one or another of us might slightly favor one or another explanation over another. At this point, however, we don't really know.