>If your model contains infinities, it's automatically unhelpful; that takes you into Pascal's Wager territory. If the damage is infinitely bad, then it it would justify draconian measures against even trivial risks of too many plastic bags. But however bad they are, they're not infinitely bad. Such a model would justify arbitrarily high bag fees, not some piddling ten cents with the hope of changing long-term consumer behavior.

Sometimes that's the reality of the situation, there are things that cannot be priced. That's why we don't consider a murder tax an acceptable way to deal with homicide.