This is kind of like worrying that God might just decide to kill everyone some day. There's nothing you can do about it, so it's best to just forget about it and hope that by the time a civilization is advanced enough to build such technology they also have advanced ethics enough to not use it.

This used to be a common SciFi staple, that a civilization advanced enough to travel the stars must have solved their social issues first or they would have destroyed themselves with their own technology. Basically as the cost of ending all life on the planet drops you need to advance your ethics fast enough to prevent it from happening. Eventually everybody is carrying around pocket antimatter batteries and either everybody is well adjusted or everybody is dead.