I'm surprised I haven't seen more "I Don't Want to Believe"* types here suggest that people are being fooled by very popular, affordable new electric RC helicopters. They're amazingly agile in the air, able to hover and stop and do all kinds of maneuvers, and are silent.
Of course, there's a reason electric RC helicopters couldn't be the explanation of any dramatic night sightings of silent craft (daytime, maybe, but not night sightings). The helicopter might be able to ferry the weight of the lights, but never the weight of the batteries to power them.
*"I Don't Want to Believe" I hope and pray that we all live to old, old age and die contentedly never knowing the truth about UFOs, instead still having the silly arguments like we have here on blessed FR happily into our final days many decades from now. I don't want to believe they're out there ... but then, there's a lot of bad stuff I don't want to believe. However, I'd rather be prepared mentally than ambushed, and I think that when these things/critters make themselves officially known to us, it will be the beginning of the darkest days we humans have seen. I place my faith in Christ and the Lord God Almighty.
If I didn't know better, I'd think you were a Gorebot shouting "Deniers"!
I know this might seem trite in light of your description above, but there is a difference between being skeptical of unlikely things and being a closed minded bigot. I guess it comes down to your comment about knowing "the truth." It appears that you must consider yourself more enlightened than everyone else, since you know "the Truth" but refuse to share it with us. Pray tell, how do you know the difference between someone seeing strange lights in the sky and someone seeing a spaceship from another world? Because it seems to me that all the proof we have of the latter is a bunch of grainy photos of strange lights in the sky, which kind of leads me back to option 1 as the default for these things.
It's also not fair to site pilots, astronauts, doctors or anyone else who sees strange lights in the sky and say they are any better than anyone else at this stuff. How many astronomers do we hear of seeing UFOs? How many sightings also have indisputable radar echos to go along with them? Otherwise it's just people seeing strange lights in the sky that could be anything, so the number of them seeing these things isn't relevant, nor is their profession unless they are professional people who look at the sky for a living, and even they might not know the source of some mysterious light if they saw one. Still, it's a far cry from "lots of people see a weird light" to "lots of people see alien spaceship".
As for alternatives to what these particular lights might be, I have no idea, but I'll bet there are million mundane explanations that come before "alien spaceship buzzing earthlings." You don't have to make up exotic explanations for these things either. In the past these lights have turned out to be flares dropped by planes, various types of balloons reflecting or carrying lights, flocks of geese reflecting light off their bellies, aircraft flying at an odd angles to the observer, meteor showers, and on and on and on. So, if you want to prove it's aliens, you have a long way to go.