I believe aliens have been among us for a very long time.
Carl Sagan once said:
“The universe is a pretty big place. If it's just us, seems like an awful waste of space.”
Looking at this question purely from a limited human standpoint, with current beliefs about how life itself came to exist, let alone what other forms of life might exist elsewhere in the universe, that is a reasonable question. We are barely a speck of dust, compared to the "house" we live in and the "suburb" where our house is located, let alone the country or the world.
The vastness of the universe makes no sense under presently accepted "scientific" scenarios.
But as a Bible believer, we see this scenario in a completely different way. We believe that we are the very beginning of a monumental process that was going to take forever to accomplish. The vastness of the universe only makes sense if there was a purpose to it from the beginning.
The Bible itself speaks of the existence of other lifeforms, though not material in nature. They have interacted with us through history. It helps to understand that angels are not fairies.....they are powerful spirit beings who serve the interests of the Creator.
All the stuff that went wrong in the beginning was covered in the timeframe given for the Creator's first purpose to be realised. Once he has sorted out all the "bugs" that naturally go with the appropriate use of free will, laws would then be created about the behavior that would govern all intelligent life to come.
Once the world we live in has been perfected, and comfortably filled to capacity, I personally see no impediment to the Creator making other worlds inhabitable and space travel becoming the norm. What would prevent it?
It doesn't make sense to me that life is an unplanned fluke and that our educational advancement is just an accident either. I see it as all carefully planned and executed just as the Creator foretold in the beginning. Free willed beings have to see that compliance with certain laws is the way to stop rebels abusing the free will of others. We are proving that it is a difficult lesson to learn when we see the majority of people today controlled by the will of people we disagree with. Our history is filled with abuse of power. It doesn't benefit anyone. The Creator was always the best one to listen to....but we had to find that out for ourselves.
The vastness of the universe is not without purpose and that purpose has forever to unfold....whatever that may be. That is what makes sense to me.