> Do you believe that, given a million dollars for every bag used, the government could clean up this supposedly irreversible damage?
You're missing the point.
If you charged a million dollars for every bag used then basically no one would use plastic bags. Or at least few enough people that the aggregate environmental impact would be negligable. As it turns out $5 or $10 would probably work as well as $1M.
The whole point is that it's totally impossible to come up with realistic estimates for something like plastic bag waste. So you set the prices high enough to disincentivize their use.
The purpose is the disincentive, not actually putting accurate prices on externalities. Confusing these two things is the source of the confusion in SilasX's original post.