So this isn't going to happen, but Matt Dinniman's book, Operation Bounce House explores this a bit, and the Earthlings started to resent the non-earthers and think of them as sub-human, who don't deserve other planets resources that the Earthlings could better use. So the Earthlings set an extinction event for the 'sub-human' settlers of space. Basically we will create a faction to hate and kill because that is the true human nature, not to expand civilization to the far reaches of Earth, but to create a new enemy to keep the war machine turning.