I guess the goal is to only penalize plastic when there is a good alternative. For example, cars have a lot of plastic in them, but they make them a lot lighter

I guess the goal is to only penalize plastic when there is a good alternative. For example, cars have a lot of plastic in them, but they make them a lot lighter and more fuel efficient, so you might not want to tax that plastic. It would be borderline impossible to write a general law that describes when plastic is ok and when it isn't, much better to issue practical rules on a case-by-case basis.