^ and the evidence is? The Earth is flat so there can't be aliens?
You don't need to see something to believe it exists. Most people never been to China. Should atheists not believe it exists until they see it for themselves or something? What we understand of how the universe works makes it probably true that aliens exist. Just like life exists here. It's not inconsistent for atheists to believe that.
& i specified atheists because they don't believe in God that they can't see it so it is ridiculous to believe in aliens while there's not a single proof of their existence. 
You don't need to see something to believe it exists. Most people never been to China. Should atheists not believe it exists until they see it for themselves or something? What we understand of how the universe works makes it probably true that aliens exist. Just like life exists here. It's not inconsistent for atheists to believe that.