> It's pretty rational for someone to understand that and make personal choices without feeling like they're causing real danger to the community.

Discounting externalized costs to zero is rational, true; that's the source of the tragedy of commons (in the economics/game theory sense, not necessarily the somewhat disputed original example for which the effect is named.)

But that's a manner in which individual rationality is insufficient to address issues whose effects aren't limited to the individuals engaging in transactions.