What are you talking about? Do you wish to live in a human society? Litter of plastic bags is an externality - all this law does is to impose the costs on those who incur it.
There is a suggestion that ultimately a bank doesn't put you in jail, where governments can do that if you continue to not pay fines. But increasingly governments take unpaid fines from income tax refunds or other mechanisms for collection rather than consider outstanding fines a criminal offense rather than civil.
That would depend entirely on whether the bank and its customer had agreed upon it before hand or not, wouldn't you say?
As far as I can see, that is orthogonal to the issue at hand.
> all this law does is to impose the costs on those who incur it.
We might consider littering to be immoral, and might therefore feel that we have a right to prohibit others from doing it, but it does not follow that we have a right to prohibit people from using, selling, owning or manufacturing bags (or fine or tax them for doing those things).