You say that with a fair degree of certainty, as if it is a fact when as far as I can tell it is merely conjecture unless you've got some irrefutable proof that you've been saving for just the proper occasion?
No proof, just a belief.
A belief that there are living sentient beings out there.
People believe in an almighty powerful being who watches over us and created the earth and life etc.. but they can't believe in another sentient species somewhere in the galaxy? It baffles me who closed minded some people are

And put it this way, isn't God* technically an alien?
*If he exists.