Smokers have little net financial impact on the rest of us

Mankiw, in a NYT article on sin taxes:

Sometimes, advocates of “sin” taxes contend that consumers of certain products impose adverse budgetary externalities on the rest of us — that if the consumption induces, say, smoking- or obesity-related illness, it raises health care costs, which we all pay for through higher taxes or insurance premiums. Yet this argument has a flip side: If consumers of these products die earlier, they will also collect less in pension payments, including Social Security. Economists have run the numbers for smoking and often find that these savings may more than offset the budgetary costs. In other words, smokers have little net financial impact on the rest of us.