Ray (about to start the strangest evening of his life) says :

Time travel. It'll turn your brain into spaghetti if you let it. Best not to think about it. Best just to get on with the job in hand. Which is destroying the enemy before they're even born and have a chance to threaten us. We're expecting any resistance to be light, because the ancestors of our enemies have yet to evolve any thumbs... or indeed spines. But that does not change the fact that they may one day evolve into a species that may pose a threat to us. And for that reason, we are going to rain down a fiery death upon them that will turn the surface of their planet into a radioactive desert! Because we are the planetary peace corps! And that is what we do! Now, are you nappy-wearing motherfuckers ready to lock and load, and get it on?