Sagan proposed that advanced galactic civilizations eventually wipe themselves out in nuclear wars.
. .But think what one insane individual could do to a planet with sufficiently cheap and available nanotechnology.
[More likely, advanced galactic civilizations will wipe themselves
out by subverting the respect for truth in science to the expediency
of promoting political fads.
Just think what one individual could do to a house with sufficiently
cheap and available gasoline. It's a good thing we don't all live
in the same house...
--JoSH]