Myself: I can't help but wonder about anthropic effects here. It might be the case that nuclear-armed species annihilate themselves with high probability (say 50% per decade), but of course, all surviving observers live on planets where it hasn't happened through sheer chance.

Just to expand on this (someone please stop me if this sort of speculative post is irritating):

Imagine there are a hundred Earths (maybe because of MWI, or because the universe is infinite, or whatever). Lets say there's a 90% chance of nuclear war before 2008, and such a war would reduce the 2008 population by 90%. In that case, you still end up with 53% of observers in 2008 living on an Earth where nuclear war didn't occur.

This implies that we might be overconfident, and assign too low a probability to nuclear war, just because we've survived as long as we have.

But: The argument seems to implicitly assume that I am a random observer in 2008. I'm not sure this is legitimate. Anthropic reasoning is irritatingly tricky.