It does not seem plausible that we live in a supposedly infinite universe, and that by complete coincidence we are the only beings or life form to exist in the entire universe. Scientists have found "goldilocks" planets many light years away that show the same features as earth. It has even be said that some planets we know about have many features that allows it to be possible for life to exist.
I'm not saying I believe in little green men with big alien guns, but there has to be some sort of life form out there, whether it be some sort of plant or just something that respires or can be considered to be "living."
It is essentially impossible to reside in a universe with billions of stars similar to our sun, each with their own respective galaxies in orbit, and not believe in other intelligent life in the universe. While our planet has perfect conditions to support carbon-based life forms, other life forms might also have suitable habitable zones that is sufficient for other forms of life.
The universe is a big, big place. Even our own galaxy has an estimated 100 billion stars with billions more planets. In all of those places, surely there is at least one more with alien life on it, even if it is primitive and not sentient. Some alien life must exist somewhere in the "goldilocks" zone where water and oxygen coexist much like on Earth.