The Vex are the good guys. I know this statement can come across as a bit shocking, but hear me out. [spoiler]The Vex are biological robots which can travel through time and space that are [quote]"...thought to be buried within every celestial body. Linked by a network unlike any on Earth, they operate in unison, directed by a single unfathomable purpose."[/quote] These machines arrived with the Darkness and during the collapse transformed Mercury into one of their machines. However, it appears the Vex have dormant networks under every planet, just waiting to be revived. [quote]"According to Ishtar Collective records, Vex are capable of generating simulations of real-world events with perfect fidelity and predictive ability - essentially running a parallel reality in their minds which is arguably indistinguishable from the "real" universe."[/quote] My theory is that the Vex have been to the future to see that humanity has become the most evil race in the galaxy, most likely do to the arms race against the Darkness. Humanity is most likely oppressing or destroying any alien species that poses any sort of threat to prevent a second Collapse. The Vex returned to the past and ran their simulations to determine what the best course of action is to help all the species we hurt or destroyed. Sadly for us however, the best course of action is to remove us and other war focused species like the Cabal or scavenging species like the Fallen from the universe. This may seem hypocritical as this would make them a war focused species, but the difference is the Vex are fighting not only for their own survival like the humans are, but the survival of species we humans have yet to encounter.[/spoiler] So there's my theory; please add to or help revise as you wish. Thank you for your time Guardians. *Please note everything posted here is opinion based on a combination of in-game facts, speculation, and my own personal opinions. Constructive criticism welcome.* [b]Sources:[/b] Vex Grimoire cards http://www.destinypedia.com/Vex