30% by mass not by pollution. The speculative aim of the legislation is to decrease pollution. It's a bit like saying alcohol abuse will go down if we ban alcohol (when the opposite happened, hardcore liquor prevalence and potency
increased which increased alcohol abuse).
Coase theorem shows that increasing transaction costs increases externality costs.
https://en.wikipedia.org/wiki/Coase_theorem
If you ban the giving out of thin-plastic bags because they feel bad, and then the market moves towards giving everyone a thick (more environmentally taxing and ecologically costly) 'reusable' bag, you've made the environment worse not better (despite it feeling better). Case in point: the number of times a bag needs to be reused before it was less ecologically costly far exceeds the life of the bag.