“Do you believe in UFOs?” is often asked. (Also “Do you believe in Bigfoot?”, “Do you believe in flying saucers?”, “Do you believe in aliens?” etc.)
UFOs exist. You can’t “believe” that they do, or even hold the opinion that they do. Or, that they do not. They do, the same as cars and houses and toasters and dogs and cats and microwaves exist. “Belief” has nothing to do with it.
One can believe that extraterrestrials exist. I believe they do. I’ve never seen an alien, and my opinion, which admittedly verges on “belief” or at least, a very strong opinion, is based on a life long journey of data collecting, and, I suppose, a bit of faith. Nothing wrong with the latter whatsoever. I’m not saying it’s fact, and I have no desire or need to prove anything to anyone.
Still, even though I may “believe” that extraterrestrials -- or some sort of entities, extraterrestrials or other -- exist, I don’t believe in them. There’s a very huge and very important distinction between the two: believing that a thing exists, and believing in that thing.
If ET exists (or whatever entity) I wouldn’t “believe” in it. Any more than I believe in my cat. Or my stove.
While there are those who have created religions around ET, believing that they are a new form of “God” usually in the Judeo-Christian framework, the use of the word belief can’t be used so carelessly, and that belief can’t be assumed.