First of all, your question implies that the reader does in fact believe in extra terrestrial life, which the reader may or may not believe.
I have recently researched the subject of alien life elsewhere in the universe, and people with more knowledge and experience in that area than me insist that they do indeed exist. Former astronauts, IMHO, would know better than anyone what they are seeing when they are in outer space. They would know if what they are seeing is natural phenomena or something else . . . I don't think they would lie about it. You can read my recent hub on the subject by going to my profile page and accessing it there.
I have had some experiences that could not be explained by natural phenomena, but I prefer to keep them to myself. Sharing them would not benefit me at all, and they would be unlikely to have any affect on anyone else either. I could provide some personal experience, but to what purpose?
Lots of people think even our astronauts are funny in the head when they talk about aliens from other planets. A lot of people must experience extra terrestrial beings and/or strange occurrences/events for themselves before they will believe. Even then some people may doubt and deny because they can't handle the idea that we are not alone and that we are probably existing at the pleasure of creatures far more intelligent/advanced than we are who have the ability to obliterate us at any time. Hard for some people to function knowing that, so in order to stay sane and sober, they just live in denial.