You don't think there is anything else out there, that earth is the only planet with intelligent life? Might be true.
What do you think your reaction might be if it is proven to you there is extra-terrestrial life. Does it change any of your other beliefs?
I need to witness something to decide and believe in it. In that case, my belief may change.
In 2-3 decades, a telescope in space will detect in the spectrum of exoplanet atmospheres those elements that indicate signs of life. We will know exactly where there is primitive protein life (perhaps not only primitive).