In the 1967 movie The Graduate, a baffled Dustin Hoffman is given just one word about his future from a family friend: “Plastics.” He doesn’t go with it, which may be just as well. Plastics, which have done so much for us, are a two-edged sword.

France just became the first country in the world to enact a ban on plastic dinnerware. As of 2020, French picnickers, in lieu of plastic plates, cups, and cutlery, will have to use bio-sourced, compostable equivalents—or perhaps return to the old-fashioned wicker picnic hamper, packed with reusable china, silverware, wine goblets, and after-dinner coffee mugs.

The new law is a subset of France’s 2015 Energy Transition for Green Growth Act, a sweeping initiative designed—in