system
Given the following post, respond as if you're commenting on Reddit:
human
[WH30K] So why does this Emperor guy hate Xenos so much?

Alright so yesterday some intergalactic space ship pulled into orbit and sent down a legion of metal men handing out pamphlets encouraging us to be annexed into "The Imperium of Man" as part of their "Great Crusade". Sounds great not being alone in the universe but under point 8 of their leader's mission statement he called for the complete annihilation of all alien life. Seems pretty absurd that he accepts all humans but won't give **any** xenos a chance? Take our natives, we've lived beside them for hundreds of years without conflict and we've managed to form an interdependent society. How does wiping out our neighbours benefit mankind? 

*For those who didn't notice, this is set during the Great Crusade. It is canon that humanity was more rational and less ignorant, so simply responding with HERESY! -BLAM- wouldn't fit as a response.*
gpt
An interpretation I've had is that the Emperor doesn't necessarily demand the complete extermination of all Xenos in the Milky Way. He only wants the best for Mankind, which means that non-Humans must be kept under some sort of control, seeing as aliens have been more than willing to subvert humanity or attempt to outright destroy it. The Jokaero, the Kinebrach, the Eldar, the Greenskins, the Megarachnids, and the vast majority of aliens that Mankind has encountered across the stars all seem to be particularly dangerous, and have refused any attempts at segregation or imposition of order on behalf of Mankind. 

It's bound to be true that not every Xeno wishes to see humanity burn and crumble, but it's also not worth the risk to let the few who do find quarter within Mankind's grasp. If non-humans can't be contained within specific planets/systems, then the only control we can impose upon them is through a brand warfare which ends with their extinction.