I really can’t imagine an argument that plastic is not harmful and doesn’t kill millions of birds and marine mammals very year. Organisms that grow directly on the plastic I would imagine are most comparable to weeds, they may be native but still crowd out more biodiverse species by growing, reproducing and dying quickly.
Just one more example where “scientists” thought they knew everything about this, but yet again, are surprised that it’s occurring.
I saw a story years ago that there are critters that eat the coating on cd’s. This was when cd’s were considered to be good for long term storage but turned on they are just dinner plates for creatures to dine off on.