There a definitely strange things seen in the sky at times. No doubt of that.
Some of them we can easily dismiss. A light high up moving in a straight line? Probably a plane or, more rarely, a satellite or fireball.
Some are not so easy to dismiss. A light making weird maneuvers high up? Stranger. An object seen close-up by a reliable, credible observer like a pilot? Definitely merits some scrutiny. Abduction reports by someone with no history of mental illness or delusions? Perhaps.
However, even these latter cases still do not mean we are dealing with aliens. They simply mean that we are dealing with phenomena that we do not understand. Other explanations remain possible so long as the phenomenon remains unexplained.
The root problem is that relativity continues to remain our best explanation of the universe at a macro level and it does not allow objects to travel faster than light. While it is possible that aliens could have created something like
an Alcubierre Drive, that is still a theoretical construct that we are not sure actually works and that we will not be able to test for decades or even generations because of technological limitations.
So if they are aliens, they are either local (ie. from Earth or somewhere in our solar system) or arrived via slower-than-light technology and set up a base/colony here. Not impossible, but not something we have any single shred of real, solid evidence for, either. Extra-dimensional beings are even less likely, since most multiverse theories do not allow for travel between universes. Occams' Razor suggests we start with the simplest explanations: natural phenomena and human phenomena (e.g. experimental aircraft and such) before hypothesizing more complex, difficult ones (e.g. aliens).
So, what are they? I have no flipping idea. Having never seen anything that struck me as truly mysterious and unexplainable in the sky, I'm pretty much an agnostic on whether UFOs are anything more than misidentified human and natural phenomena. Which is a bit of a change for me. Up until my twenties, I was a bit of a believer where UFOs are concerned.
OTOH, I am quite sold on the possibility, even probability, that there is life on other planets, moons, etc. The basic chemistry behind life (water, organic compounds, etc.) is found everywhere we look in the universe. There are likely hundreds of millions of planets in our galaxy alone and a non-zero percentage of these are Earth-like, meaning life as we know it could exist. Further, research into "extremophiles", creatures that live in environments previously thought hostile to life, shows that life is much more persistent and pervasive on Earth than we previously knew and that we need not confine ourselves to looking for Earth-like worlds in searching for life. It has opened us up to the possibility of life in places like Enceladus and Europa (moons of Saturn and Jupiter respectively) rather than just on Earth-like planets. So my money is on extraterrestrial life existing. There is just too much in its favour now.
However, finding simple, or even medium complexity, life on a moon here does not tell us about the likelihood of intelligence on other worlds or of them visiting us in strange glowing spacecraft. Scientific testing of that hypothesis is whole other kettle of fish.
