From an evolition standpoint imo, there are two major obstacles for the assumption that aliens, as we speculate them to be, should exist:
1. The formation of the first cell is as equally random as the universe itself.
Meaning, the number of galaxies and planets that could potentially allow life is as infinitely random as a couple thousand phosopholipid molecules deciding to encase a set of RNA, which is basically nucelotides composed of 3 more material. And this cell composition has to be 100% stable else the cell has to survive.
If we reset earth to 5 billion years ago, the chances that this cell is reconstruced again is 0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001%
You get the idea
2. Even if there is life out there, the chances that these aliens represent the intelligent creatures we picture in movies is even further lower than the percentage above. That humans became conscious and intelligeble in this manner is even a bigger mystery.
So if there are aliens out there, they'll be dumb as shit most likely. Just a random arrangement of cells like this fucker for example
That said, aliens existing is much scarier.