COMMENTARY For decades, public health advocates have championed harm reduction for people who cannot stop taking health risks — or do not want to. Needle exchange is a classic example. Intravenous drug users get clean needles because, the reasoning goes, contracting and spreading AIDS is worse than making heroin use a little easier. But harm reduction for hard-core smokers is another matter. At issue is a form of smokeless tobacco, a popular Swedish product called snus (rhymes with loose) that satisfies smokers' nicotine addiction with negligible health risks of its own. But to many foes of smoking, it is not...