[Kaj]

Where do all the plastic bags used in SF go (those not recycled)?

They go buried somewhere in SF. Where they stay for hundreds even thousands of years. Thus the true cost of plastic bags is borne out by future generations and the rest of society -- in other words, your cost analysis completely externalized the true cost of plastic bags.

Thus if SF'ans want to protect their citizens and future citizens from dealing with such external costs, there can be a legitimate case. There are thousands of cities to choose from if you disagree. And if you want to stay and persuade others to change the law, it is much easier at the local level. The knee-jerk reactions against the decisions of local govt fly in the face of real democracy. Now you may not like local-level democracy, but no better alternative currently exists. And when an anarchist alternative does emerge, I wouldn't be shocked to see local communities develop and enforce their local values. In actuality, it would be inevitable, and that is okay.