I'm not religious, so I can chime in as someone who has a deep knowledge of astronomy/cosmology and evolutionary biology, and I'll base my arguments off of that as well as the assumption that life started on Earth naturally rather than God. If God did create the Universe I'm likely to think he "let it do it's own thing" and orchestrated life to evolve on Earth organically...but that's another discussion. Anyway.
Most people insist there "must be" life in the Universe based off probability alone. There are billions of galaxies, each with billions of stars, each star likely having planets..."just do the math" they will say. But recently some astronomers have been outspoke critics against this, but they of course barely get any attention. The basic counter argument is quite simple: if life arose on Earth due to abiogenesis, we have absolutely no idea how probable that is since we have a sample size of 1. Survivorship bias makes it seem like it must be likely, especially since it happened in a relatively short timespan. But we really have no idea. If the odds of abiogenesis are 10^24, then there very well not be any life in the observable Universe. This of course doesn't even account for the conditions necessary for the life to evolve into complex life, and then space faring civilizations, which could also be astronomically low chances due to "great filters" ending life on the planet, such as cosmic rays, asteroids, civil war, malevolent tech, etc.
In short, people are too optimistic. As it stands, we have no evidence of aliens. The fact that the US Govt says they've encountered them means they haven't, because they lie about everything. Personally, I believe the US government is obsessing over them because they have too much waste and many govt offices do nothing but sit in offices and watch Youtube all day. It's also possible they're just doing it to distract the citizens from its deep economic and social problems, like a psyop. UFOs have many possible explainations besides "aliens", some of which are quite interesting.
It's likely either that life is extremely rare, or extremely common, and it's probably not the latter since we've seen zero signs of it. It wouldn't even be hard to detect - we could detect planets with "biosignatures" such as oxygen rich atmospheres, and we've yet to do so, and sure, some aliens might be so exotic we wouldn't even be able to recognize them as sentient life, but that's highly speculative, albeit interesting. People argue we've hardly looked for very long or haven't looked very far, true, but we're in the part of the galaxy that is most likely for life to occur (the core is too dangerous) and we've seen NOTHING whatsoever in decades now. Will people still make this argument in 100 years?
The most realistic estimate that I heard is that there is one civilization per galaxy, which seems possible, but it's also very possible we're the first intelligent life in the Universe. People hate this idea though because they hate themselves and project it onto humanity as a whole which prevents them from letting themselves admit they may be special, and insist that's arrogant. The mediocrity principle also comes into play. In short there is a lot of emotional arguments people make for why they believe in aliens, and they're pretty flawed.
Oh one last point. People will say the Universe is may be infinite. If that's true, it doesn't matter. The fact that the Universe is expanding faster than light means we will never be able to reach anything outside of what we can currently see (ie the Observable Universe), because everything is moving away from us faster than light speed. So if the Universe is indeed infinite, we're effectively alone, even if life is teeming in the infinite expanse outside of our observable Universe. Personally, if you believe we're the only life in the Universe it makes us truly feel important and special and there's nothing wrong with that. Assuming life must be everywhere devalues our existence. If we somehow knew life did not exist in the entire Universe, our perspectives would radically change for the better, and we might finally be able to value our lives enough to build a proper civilization.