This paper is awful from a scientific standpoint. Rather than sticking to facts, it's full of opinionated judgements, logical fallacies, and poor use of statistics to back up claims.
A lot of it is devoted to caricaturing arguments for plastic bag bans and "debunking" them. For example,
> Are Plastic Bags Killing Millions of Marine Animals?
It's also full of logical fallacies. For instance,
> By any measure, plastic bags constitute a small proportion of all litter. So, it would be foolish to focus any strategy intended to reduce litter primarily on plastic bags.
Apparently this is meant to imply that no effort at all should be spent on reducing plastic bag litter.
For instance if you look at Section 2.3 and the bottom of page 18, it cites reports that Americans throw away 100 billion plastic bags per year, then says "A look at the data, however, reveals a very different picture." It goes on to give data that in no way contradicts that figure, but instead focuses the argument on how small a fraction of the mass in landfills comes from plastic bags.
The abstract gives 6 claims, e.g. #1 is "The bans, fees and taxes on shopping bags have a minuscule impact on litter." But the paper is not organized so as to actually go through a demonstrate these claims. You cannot figure out from the introduction or Table of Contents where in the paper one of these claims will be demonstrated, if anywhere.
The support is disappointing due to goalpost-moving, e.g. the main supporting evidence for #1 is that plastic bags only make up a small percent of litter, therefore nothing we could possibly do involving plastic bags can have a large impact on litter.
I could go on, but it's not worth any more time. I'll just close by mentioning that the authors reveal themselves at the end of the abstract, when they write
> Those people who are genuinely concerned about reducing litter and other
environmental problems should focus their efforts on solutions that have been
proven to work.
Pretty clearly the authors are not including themselves in the list of people who are genuinely concerned about reducing litter or "other environmental problems".