> isn't this just moving to another extreme?
> It seems like both quality and efficiency have their place,
Actually, I would agree with that for sure. The real world is grey, and multiple things are true at once. I'm certainly guilty of leaning to the other extreme here.
> some aggregate of environmental impact metrics e and the number of times we use the bag n
I believe I understand, and I appreciate the overall push back.
But starkly put, and to be a little flippant ..
> would you still favor the cotton bag just because it is higher quality?
.. absolutely yes. Certainly in this case. The reuse number is incredibly (incredibly) flexible. In no world n=1 will be a given. The only reason we have reuse of one for a bag, is out of habit, simply put. Habits change all the time. A cotton bag will not have a reuse of one. It is more expensive to begin with. It could hold sentimental value. It may have a lot of other uses. Do we even need a bag? 80% of time, the store clerk gives you a bag out of muscle memory, not because you can't hold a couple of items in your hands or stuff in your pockets. The utility of a plastic bag might even be closer to 0 than 1.
> It's maximising a single (ill-defined) metric as well, no?
I think that is where we might disagree the most. Quality cannot be measured, it can only be known. I hate that this reads as touchy-feely, but I don't know a better way to put it. Once you accept that quality cannot be measured in numbers, it is liberating. Then it allows you to argue in a different paradigm; How your neighborhood "feels" because there's no plastic bags stuck in roadside shrubbery, the peace of mind knowing that your drinking water doesn't have microplastics in it, ... that's genuinely immeasurable. Yet it is the stuff that makes up quality of life. People can be convinced of those qualities, and their value, _without_ quantifying them.