If it's an existential risk, it kills everyone, selfishness suffices just fine.
A selfish person protecting against existential risk builds a bunker and stocks it with sixty years of foodstuffs. That doesn't exactly help much.
The quality of life in a bunker is really damn low. Not to mention that you presumably won't survive this particular risk in a bunker.
Another month has passed and here is a new rationality quotes thread. The usual rules are: