No need to bother. We're self-destructing without anyone having to send anything.

What a wild counter-idea. "Go back in time and kill Hitler": played out. "Go back in time and clash with the invading aliens who have sent their own people back in time to destroy us from the past by installing players that will wreck us as a species over time": oh. As I say it, this is half-way to This is How You Lose the Time War