Yes, and that's fine, but it's also somewhat a different problem. One that is better solved with a deposit scheme, redesign, or some other method than tax and ban. (Edit: or the obvious- using biodegradable additives in HDPE at a marginal cost.)

Make them twice as thick. Melt a weight into the seam of each one to prevent flying and floating. You'd still be a magnitude ahead of the alternatives. There are alternatives besides banning.

They have their problems, but people don't realize what a damn miracle of engineering HDPE bags are. And other disposable paper and plastic items, to a lesser extent.

I disagree that it's a different problem. There's a branch of corporate environmentalism that says, hey, look, green things are great when they reduce costs. LEED certified buildings reduce energy costs, for example, so everyone is down for building and occupying them. It's great, because it's a win win, but it's not at all the whole story.

Plastic bags in the ocean are an externality, whose cost is hard to measure but is paid in the lives of wild things. The whole point of externalities is that people aren't bearing any cost for them: tax and/or ban is absolutely a reasonable approach to handling them, since it makes people take literal account of the literal downstream effects.

One more thing, on edit: the analysis you're calling for is good to do, but is also prone to the "seeing like a state" problem. The analysis will only include what can be easily measured... Which can leave out a lot of the story.

LCA's are only as good as the person who performs them. But we'd be much better off if everyone at least knew what they were, and what they try to accomplish, specifically capturing all of those externalities.

Re: the tax and ban... Tires and lead batteries in most states in the US is good example of this. You can tax or ban or regulate to put a cap on the problem. But if you want to collect the existing waste already out there, an incentive refund accomplishes much more, in less time.

> Make them twice as thick. Melt a weight into the seam of each one to prevent flying and floating.

Well, now a palette of them weighs 2-10 times as much and the energy required to ship them needs to be recalculated.

Sure. That's the point. There are lots of variables that all need to be looked at and evaluated to find the sweet spots. It's why LCA's should be done for every option, including a ban. Identify what variable(s) are the low fruit to go after.

> One that is better solved with a deposit scheme

Ocado will pay 5p per bag, even other supermarkets' bags.

You also have to make the deposit amount high enough to convince people to use the mechanism.