I don't believe it. But, like I said, it doesn't cost to entertain the possiblity. It's great fun, and cheap entertainment.
Besides, I personally believe there are others out there, somewhere. Now if there has been contact, that's a whole different story.
I personally enjoy the speculation that we are "seeded" here, chariots of the gods type stuff.
And not that doesn't preclude a belief in God, I just don't believe every word of the Bible is to be taken literally.
Additionally, their interaction with humans has been far from benign. Abductees are psychological scarred from being plucked against their will over a long period of time and for what seems to be sexually oriented experimentation with a possible goal of genetic engineering. All abductees described the experience as "rape."
I ascribe more to the theory that these visitors are the same creatures that have been visiting earth (or humans, at least) since the beginning of recorded time. Even Genesis and the apocryphal Book of Enoch makes mention of such creatures.
Long story short, some people believe, from their MO of abduction and genetic manipulation that they are "the fallen" who are hurriedly trying to create a hybrid we might otherwise know as "the Beast" or "the AntiChrist."
Boo!