The main reason UFO reports are universally dismissed by skeptics is that the quality of the reports usually reveals a failure to properly evaluate and describe aerial phenomena. At the very least, they are so incomplete and contradictory that even if the witness HAD seen a truly extraordinary object, it would be impossible to deduce the fact from the description.

For example:

It is impossible to tell how large or high up a distant unfamiliar object is. Reports like "a mile long", or "bigger than a supermarket", "a thousand feet up" are worse than useless because it is impossible to know how far away the object is. A better way to indicate apparent size would be to say "it was three degrees across", or "the size of my clenched fist at arm's length".

Descriptions of distance and speed are also intimately dependent on a knowledge of the object's true dimensions and shape. A proper description would relate something like "it traveled from zenith to horizon in less than 5 seconds", or it appeared about 20 degrees above the southwest horizon, traveled due east, then made a right angle turn to the north, disappearing almost directly overhead." How often do you hear a typical UFO witness say something like "it appeared to be a bright white star traveling in a great-circle course from NE to SW, at about a degree per second"?

It is very easy for honest but inexperienced observers to get very excited and mistake perfectly ordinary and recognizable objects and to extravagantly embellish them. I have seen otherwise reasonable individuals standing right beside me give fantastical descriptions of perfectly routine phenomena which I immediately recognized and identified at a glance, and then argue with me that I was mistaken because I disagreed with them.

When you talk to someone and get their story, it is often possible to get useful information from them by careful questioning. But be very careful, anyone who has actually tried this knows how easy it is to put false memories into someone else's head by suggestion. When people are excited or scared, they want to believe, and they want you to believe them. A scared witness (and I've interviewed a few) will latch on to anything you say and elaborate on it in an attempt to get you on their side. It's just human nature.

When someone relates to you their questioning of a witness, it is impossible to believe them. This is not because the witness or the reporter are dishonest, but because you are now getting pure hearsay. It is impossible to cross-examine or personally evaluate the original source of the observation, and things tend to get lost or embellished in translation. If the reporter is a believer, or someone who wants to believe, this is doubly so. Again, not because they are necessarily lying, but because they are influenced and open to suggestion too.

Sometimes witnesses and/or reporters DO deliberately lie. This immediately makes all the good reports immediately suspect. The more a report is likely to be a lie, the more complete and detailed it is likely to be, a difficult situation for any detective! The liar will have an agenda, he will be as convincing as possible. In this environment, no third-hand report can really be trusted. If the report describes an appartion that can ony be described as an alien spacecraft (portholes, metallic, symmetrical, "under intelligent control") it is either an outright fabrication or the real thing. A proper conservative evaluation always demands the former pending corroborating evidence.

That the earth is being buzzed by alien spacecraft, although highly unlikely for a variety of reasons, cannot be ruled out altogether. After all, it violates no accepted physical law. Still, "extraordinary claims require extraordinary evidence". The burden of proof must always lie with the challenger to the current orthodoxy. "...you can't disprove what I said" does not count as proof. Neither does "...where there's smoke, there's fire".