By that metric, what is the environment and why is it important to protect it? On an abstract enough scale, we and our plastic are simply evolutionary products and the fact that we are wiping out species and cataclysmically heating the planet is just a geological event that might be called The Great Human Extinction by some distant inteligent race.
All irrelevant to the comment: how 'pretty' the creek is, is not an ecological metric of merit. Its all about Ph, CO2, erosion and a hundred other things.
Keeping the planet livable and diverse is no more objective than keeping it plastic free. Ecology is by definition a human value, the universe doesn't care about CO2, biodiversity or erosion anymore than it cares about plastic bags.
(But sure, subjectively, plastic bags are a lesser concern, because they merely inconvenience us and trigger our empathy when a critter chokes on them, without directly threatening our own survival).
As George Carlin used to say, the planet is just fine. It's the people who are f*ed: https://www.youtube.com/watch?v=7W33HRc1A6c