Our world contains a vast array of opinions regarding extra terrestrial life. To some people, it's almost arrogant to say we even could be alone in the universe. Some even claim to have encountered such beings themselves. Many people are on the fence. But if you run around speaking about aliens and UFOs and the like, you're inevitably going to encounter many people who will think you're a complete and utter nutter.
But I submit that we all believe in UFOs. I remember one time, when me and my brother were very small. He was arguing with mom about something, though I can't remember if he was objecting to bath time or bed time. What I do remember is that the argument took place outside the bathroom. During the argument, a crane fly erupted from behind a curtain, and immediately, my brother began to panic. "It's a flying thing! It's a flying thing!", he screamed, running around in terror.
Of course, to me, now, the "flying thing" is very much identified. But to my ignorant, scared little brother, and even to my own young eyes, this was an unidentified flying object. That's right, with my own eyes, I have personally encountered a UFO.
What you have just read is a nigh perfect example of the fallacy of equivocation. That is, the use of ambiguous language within an argument. In the above example, I applied two different uses of the term "UFO". With regard to the extra terrestrial life debate, UFO typically refers to some kind of unexplained, airborne phenomena that is typically explained as alien activity. Most often, it is assumed these UFOs are the alien's spacecraft. This is radically different from the "flying thing" that me and my brother encountered in our youth. My belief in crane flies does not require me to believe any life forms exist outside of Earth.
In religious and political debates, equivocation is a very common fallacy. For example, Evolutionists frequently attempt to define Evolution as simply "change over time". The obvious problem with this is that, by this definition, Christians can believe in both Evolution and the historical account of origins found in the book of Genesis. But obviously, there is a conflict between the Biblical and Evolutionary views. In the book of Genesis, God created everything over a course of six days, with biological life being created, according to its kind, on days 4 (plants), 5 (water and sky life), and 6 (land creatures and man). But in the Evolutionary narrative, everything began as a singularity, which exploded millions of years ago, forming the cosmos over time. Eventually, the sun formed, followed by our Earth, which eventually spawned a single living cell, which, via gradual modification over many generations, eventually became all the life we see today.
Just as there is a difference between UFOs and UFOs, one referring to alien spacecraft, the other to any flying object we just don't know about yet, there is a very obvious difference between the theory which states "...that many living animals can be observed over the course of time to undergo changes so that new species are formed", and "...the theory that all the living forms in the world have arisen from a single source which itself came from an inorganic form."
The above quotes come from Gerald Kerkut's book "implications of Evolution", wherein he quite adequately distinguishes between what he would call the "special" and "general" theories of Evolution. To equivocate the two is misleading, and the unacceptably high number of Evolutionary apologists who do so are guilty of the equivocation fallacy.
Perhaps the easiest way to respond to this fallacy is to commit it in turn. This is perhaps harder to do in the UFO discussion, but with regard to origins, it is really very easy. See, while Creationism rarely refers to anything other than a religious view of origins, "Intelligent Design", of which Creationism is a form, is more commonly used. The clue to the meaning of Intelligent Design is in its name. You can't not believe in intelligent design, as right now, you are reading an intelligently designed article, written in an intelligently designed language, on intelligently designed technology. However, your belief that humans are capable of intelligent design does not require you to believe humans are intelligently designed. Thus, when Evolutionists try to give the General Theory of Evolution a free ride on the back of the Special Theory of Evolution, we, as Creationists, can show the folly of this by trying to give Creationism a free ride on the back of Intelligent Design. When it doesn't work, the Evolutionist will hopefully see the absurdity. This approach can be applied to almost any argument which uses the equivocation fallacy.