There are not aliens among us, but if there were aliens among us, it would not be a supernatural phenomenon. I disagree completely that things can't be put into science and non-science boxes. Science is when you look for the answers, and non-science is when you make them up. Let's take UFOs for example.

There's a blob in the sky. We don't know what it is. It is flying. It has some mass. That is, by definition, an Unitentified Flying Object. It moves in ways that seem impossible, and then suddenly vanished.

Science is looking at the evidence and trying to form a testable hypothesis. Perhaps it was an optical illusion? If so, we could probably recreate the conditions and replicate the illusion. Perhaps it was a human craft that has capabilities that were previously unknown to us? If so, we could probably describe a theoretical mechanism that could move or disappear the same way. Can we prove it was a craft? Can we measure accurately its behavior? Are the instruments and witnesses reliable?

The best bit about all of this is that any of them could be true whether or not aliens exist. Once you decide that, since nothing on earth can explain it, there must be aliens with some sufficiently advanced technology, you have abandoned science altogether. Why not fairies or ghosts? Maybe it was a magician or a superhero with mutant powers? Once you abandon the feasible to assume the supernatural, you leave the door open to any supernatural explanation. Maybe the reason we haven't found bigfoot is that he has an invisible flying vehicle that defies gravity.

Maybe aliens exist. Certainly I believe that life can exist on other planets. There may even be intelligent life capable of interstellar travel. I hope we find evidence of it someday.

It strains credulity to suggest that in all of spacetime, our sentient spacefaring species would overlap with another without any measurable evidence. The evidence we do have does not support the logical leap from Unidentified to Extraterrestrial.