@kingbeauregard @gdinwiddie It might also fall into the hands of people who would zoom off to conquer another solar system or many.

If that is physically possible, it has probably happened before, and it was the equivalent of COVID or the plague on a cosmic scale. There is no defense against a relativistic projectile. You don't see it coming in time to do anything.

If aliens in UFOs really are watching earth, with special attention to the military tech, that's probably why.