A better question is why would someone be naive enough to think we are the only intelligent life form in existance
Just look at the following quote
I don't believe, its bullshit I think =)
Now, imagine this:
To limit our view, let's say in our nearby galaxy there are at least 10 solar systems similar to ours.
Now, imagine they did the same historical path,wars, improve tech, philosophy, wars, more tech.
Imagine this now: where we are now, they passed it 1000 yrs ago.
They visit us, they pass as mute people, learn our language, pass on another country and starts learning stuff, and we are been visited by them from time to time.
What about these pictures, don't tell me they all had hallucinations.
There is a race of aliens ruling the galaxy screening for races that exceed a certain level of a technological stage, disregarding such pitiful targets such as Earth.