Do aliens exist?, I think that this depends upon each individuals perception of reality. Using the currently accepted paradigm, it would seem unrealistic to believe that there are no other planets in the universe capable of supporting intelligent life. There are supposed to be billions of stars in the universe with trillions of planets. Using those numbers, it would be arrogant to assume that humans are the only intelligent beings in existence.
There are many theories about aliens having played a part in human development. Some people believe that the pyramids were built by aliens who came to assist humans to evolve. Other theories suggest than it was aliens and not God who actually created us. There are many crazy sounding theories out there and because we do not know, any one of them could be true, it all depends on the individual receiving the information.
What about the theory that all matter is basically frequencies vibrating at different speeds. This theory does not discount aliens as different frequencies and speeds occurring on other planets could materialize as aliens. This ties in to the idea that we all live in a matrix like environment. Quantum physics at this time appears to be supporting at least some of these ideas.
There are people who totally believe that the earth is flat. Some think that we live inside a sort of enclosed capsule covered by a dome that cannot be penetrated. These people naturally believe that we did not go to space and that the moon landings were faked. The flat earth believers think that God, or a benevolent all-powerful entity did create the world and life on earth, putting us at the center of creation.
Maybe there is someone out there that does know the truth about aliens, I certainly do not, do you?. If aliens do exist, and they manage to travel to earth, we can assume that they are much more advanced than us in technology at a minimum and hopefully they are more spiritually advanced. I would hope that they would see that we need some assistance and supply us with renewable cheap energy, farming technology to allow us to feed the whole world cheaply ( I think that this already exists but business multi-nationals are just not into sharing), and inexpensive, efficient medical technology, but then again they may just want us all to assimilate and become the Borg or something similar, who knows.