the only scenario I see is cans of beans becoming very cheap in terms of ammunition for unethical reasons.

Unethical even in the Zombie Apocalypse scenario? X-)

But sure, if the entire financial system {im|ex}plodes, your shorts aren't going to do you any good and so we finally achieve symmetry -- everyone is fucked.

I'm making the assumption that such comparisons are made retrospectively instead of prospectively

It is still the right way even retrospectively if you think in probability distributions. And, of course, anything "ignoring risk" is automatically the wrong way to think about the markets :-)