“In a couple of hours, I fish more than two dozen plastic bags out of the lake with my net, along with cigarette butts, candy wrappers and a soccer ball. As we work, numerous passersby on the popular trail that circles the urban lake shout their thanks, which is an undeniable boost. Yet, I can’t help being struck that our efforts represent a tiny drop in the ocean. If there’s one thing we know about these plastic bags, it’s that there are billions and billions more where they came from.” What is the author’s argument in this passage?