While I see your point, it should be noted that we are perfectly capable of killing everyone on Earth as well. The only reason this hasn't happened is because the whole world came together to be more sensible[1] about nuclear conflicts than we were about less destructive conflicts, and because of a good deal of dumb luck. And killing everyone on Earth will only ever get easier as technology advances. At least a distributed civilisation means one community self-destructing doesn't mean the end of humanity.

[1] Not a high bar, and not by much. Nevertheless, we are still (barely) here.