The message emblazoned on a walkway window at the airport in Burlington, Vermont, is a startling departure from the usual tourism posters and welcome banners: “Addiction is not a choice. It’s a disease that can happen to anyone.” The statement, part of a public service campaign in a community assailed by drug use, is intended to reduce stigma and encourage treatment. Sign up for The Morning newsletter from the New York Times For decades, medical science has classified addiction as a chronic brai