Why do people care if there are aliens or not? I think on one level, people lust for the technology that we could take from aliens. On another level, I think some people think alien visitations would be a good way to explain myths and religion.
Jesus could have been an extraterrestrial, for example. Angels could have been aliens, too. Some people theorize that there are different alien races, and that our roles as pawns in some sort of intergalactic war between these aliens might be documented in the Bible.
But what does this really solve? So we could theoritically explain our creation as some sort of lab experiment by an alien race. Our DNA might have been dumped here by aliens millions of years ago. God might just be the name of some alien general or president who made Earth his own little pet project. So what? Does that really solve the questions brought up about creation, religion, the meaning of life, and the purpose of the universe? No. It just offsets them from human problems to alien problems. If God were an alien, then who is the alien's god? What myths and religious beliefs might these alien races have? It seems like a circular argument to me.