It would be extremely presumptuous to think that in the entire universe the only planet that had accidentally enabled the development of life was our own. Therefore, the question of whether extraterrestrial life exists is a religious one until incontrovertible evidence demonstrates that it does.
The majority of religions are, quite naturally, extremely anthropocentric.. They have evolved or been inspired in peoples that perceive themselves as superior to all other lifeforms and often peoples on the planet. In the technological world we now inhabit, new religions do not occur; sects and cults develop from historic beliefs around particularly charismatic leaders without offering truly new revelations. During the times that initially created religions, humanity had a very limited knowledge of how even the earth worked, let alone the heavens. Natural phenomena were attributed to the acts of gods, pantheons of which abounded in every human culture across the planet.
Possibly life can spread across interstellar distances through bacterial spores, immune to the freezing temperatures until they reach habitable conditions. This may be so, but it will be some time before we can determine it considering our limited off-planet investigations.
Probably the most significant argument offered by those disputing the possibility of extraterrestrial life is that of "If they exist, where are they?" Although this really does not question extraterrestrial life, but the existence of INTELLIGENT extraterrestrial life. If there are other intelligences populating our galaxy, why have they not visited us in an indisputable manner? If Einsteinian space cannot be traversed at greater than the speed of light, should we not have at least detected communication signals from extraterrestrial civilizations in older parts of the galaxy, if they exist.
Unfortunately, all of our searching presumes that other intelligent species would wish to contact us. Or would at least not make any effort to hide their existence from us. Perhaps we should look at our history, examine how we have treated others of our own species based on the slightest of morphological differences and then consider again whether an intelligent extraterrestrial species would have the slightest desire to make our acquaintance.
Perhaps civilizations that have the technological capability to span stellar distances would have no problem excluding their past communications from entering the solar system. Perhaps we are legitimately excluded from the congress of sapient species. Perhaps the reason we only have unsubstantiated and unreliable reports of alien contacts are because the only aliens that are noticed visiting our planet are the equivalent of alien teenage joy riders and pranksters.