Why do (not) people believe in extraterrestrial life?

Why do some people like to talk about UFOs, giving vivid examples of their visits to the Earth, while other people donot believe that somebody "out there" might be interested in the human civilization? Was the Life on the Earth brought from far away in space by Somebody/Something or did it evolve in the normal course of time, without any interference from outside? Do "aliens" really visit our planet (and allegedly abduct people for experiments) or is it only the people's sick imagination? Why are aliens always pictured with humanlike features (with legs & hands, eyes, etc) and not something that is really unique and cannot be compared to anything on the Earth? If the "truth is out there", when will people be able to discover it?