Okay, there's time to explain. I think the Vex are actually working for the benefit of humanity. The vex "milk" contains radiolarians, which originate from Earth. The vex network is capable of being traveled by humans. The Vex just made one crucial mistake when they started to time travel: they looked where they're going. This is a no-no, mainly because it is playing dice with the universe: you could see yourself die, then you'd be required to die there, otherwise there's a paradox. The Vex looked ahead, and saw themselves killing humans. So, being machines, they examined every possibility, and decided to only do that. Why isn't Venus a machine? The Citadel erupted from the ground on Venus when humanity started exploring there! Why didn't the Vex finish the job when there weren't Guardians? They had the records on the Nexus strike. If you really wanted to eliminate humanity, you'd build a giant Vault of Glass out in space, then just teleport it around Earth, then deploy millions of Gorgons. The Vex have both the time and the resources! That could happen! Instead, when the Vex reach the point they read ahead, they'll stop attacking humanity and apologize for doing that. It'll be revealed that The Exo Stranger's in on it too. Her gun is made from materials that haven't been invented yet. What if she's from after the apology? The vex would still be putting the timeline to the point where the data matches. They have information on the Stranger. Her job is to convince the player character to fight the Vex. Its that simple. The Vex don't care. In their eyes, they're just making units for the sole purpose of being destroyed. The Stranger's group that get's attacked? That's Vex, being attacked by someone. But those are actual Vex. The ones we see are marionettes.