I think the vex are human. Lost souls, obsessed with the concept of death, because they know life is the ultimate double edge sword: with life, comes death. This is their way of controlling death. By correcting life. By unwriting life. - At the lighthouse, there is a room with a skeleton, a ripped apart vex and what looks like a vex machine, possibly for time travel. I believe it is here that a connection between humanity and the vex was made. Ever realize how once one "discovers" the vex ie) praedyth, Osiris, kabr, they never come back? Easily explained. As it reads on the robes of the exiles description: "Let the heat melt your body so your soul might flow with the river of time." —Parables of the Allspring "might flow". I believe it can happen here, but not in the way we would interpret. Our souls would be gone. What makes us human would be gone. We would no longer care for humanity, as we would transcend much further. I believe that is what happened. I believe we [b]became[/b] the vex, and now vex are attempting to extinguish us... But how could the vex extinguish their own cause? Tldr: I believe we created the vex, or we got a sneak peak of what transcends past humanity, and it didn't like what it once was. [b]edit:[/b] in avengers 2, ultron says after his creation that he "feels wrong". I believe this mentality, as an AI (exos are more psychologically advanced) could explain the theory that the vex are exos from the future. Maybe waiting millions of years resulted in emotionless exos, who also have the "hive mentality" (ants working together with a mutual goal) Exos understanding of what they are themselves (abominations) could explain their hate for what they think we are.