An odd thing happened on Facebook. My town--which is frequently at war with itself--suddenly discovered self-composure. The reason: an intrusive third party. Someone went on Maplewood Moms, anonymously, and wrote: "I'm thinking of moving to your town, but I have some questions about the public schools. The reputation is iffy. Can you elaborate?" Almost immediately, a Maplewood resident wrote, "Invader! How dare you try to sow discord? Why do you hide behind the mask of anonymity? Show yourself!" And this resulted in a pile-on. My neighbors often argue about how to get rid of a tattered flag, or how to handle the somewhat disorderly public food pantry, or how to support (or not support) the embattled high-school principal. But we can all get behind our hatred for one (maybe innocuous?) "common enemy." And so I have fondness, and admiration, for "Lemon of Troy," a classic episode of "The Simpsons." In this one, residents of Shelbyvi...