Believing in alien beings (on earth) is as stupid as believing in supernatural beings.
Please cure yourself of this disrespectful nonsense; it is beneath you and it makes you look rather foolish. I could easily compile a list of hundreds of individuals (living and dead) who believe(d) in supernatural beings and who are quite a bit more intelligent than the both of us combined. It is not a matter of "smart" or "stupid" and I think that you know better.
More on-topic, sorry Mjau, but I definitely fall on the skeptical side of things when it comes to UFO's and extra-terrestrials. Of course, I see no reason to rule it out on principle (it is not as though we could demonstrate some logical impossibility
of aliens or UFO's), but the topic is such a magnet for sensationalism, kooks, and hoaxes that it is difficult to approach any "evidence" for it with a truly open mind. Even in cases where we skeptics might concede that the proffered "evidence" is out-of-the-ordinary (strange radar readings, for example), we are likely to prefer a more mundane explanation of the facts.
I wonder why you have developed an interest in this subject, Mjau? Do you find yourself inclined to believe that there is "intelligent life" elsewhere in the physical universe? And if so, why?