This is a society you really don’t want to be in though; things have to be pretty hopeless before it’s no longer in your interest to promote a policy of cooperation.
This actually makes more sense if you reverse it! Promoting costly norms by following them yourself regardless of the behavior of others only becomes the best policy when the consequences of that norm not being followed is dire!
When I say “things have to be pretty hopeless,” I mean that the prospects for amelioration are low, not that the consequences are dire. Assuming the consequences are severe, taking costly norms on oneself to prevent it makes sense unless the chances of it working are very low.
This actually makes more sense if you reverse it! Promoting costly norms by following them yourself regardless of the behavior of others only becomes the best policy when the consequences of that norm not being followed is dire!
When I say “things have to be pretty hopeless,” I mean that the prospects for amelioration are low, not that the consequences are dire. Assuming the consequences are severe, taking costly norms on oneself to prevent it makes sense unless the chances of it working are very low.