<i>&gt; Well, you can repair the damage from plastic bags.</i><p>Maybe. Maybe not. Maybe you can, but the costs to the environment involved in doing so are prohibitive. In any case, I don&#x27;t think it&#x27;s totally obvious that this is actually possible ATM.<p><i>&gt; If your model contains infinities, it&#x27;s automatically unhelpful; that takes you into Pascal&#x27;s Wager territory</i><p>Yeah, well, reality &gt; model. Unless we colonize space, destroying earth = infinity. So the implication of your statement is that pricing is a bad model for certain types of environmental damage. However...<p><i>&gt; would justify draconian measures against even trivial risks of too many plastic bags</i>.<p>...the realistic impact of most types of irreversible environmental damage has no known bound, but is not infinite.<p>Difficult-to-bound unknowns <i>also</i> make it impossible to quantify damages a priori at the level of detail necessary for pricing. Again, reality &gt; model, so accurate pricing is a bad mechanism.<p>I think there are reasonable arguments against plastic bag bans. But trying base policy on an <i>accurate</i> accounting of the cost of long-term or irreversible environmental damage is a fool&#x27;s errand in many cases.<p>(Also, note that my point is that in general, pricing environmental externalities is weird. Plastic bags aren&#x27;t even nearly the best example of this, but <i>are</i> illustrative of the most common solution -- don&#x27;t price, disincentivize.)