The US government should encourage tobacco smoking because it helps the economy.
First, tobacco smokers get hooked and then are willing to pay outrageous taxes to get their fix. That means lower taxes for the rest of us. Honestly, that doesn't mean much for the economy because money smokers spend on sin taxes is money that they'd otherwise spend or invest anyway. It's fungible. It all comes out in the wash. In fact, the practice of smoking wastes resources, actually weakening the economy. But any proposal that includes the phrase "lower taxes" gets a lot of positive attention, especially here in Washington state.
Second, tobacco smokers kill themselves off before they can retire. They work productively during young adulthood and middle age, paying dutifully into Social Security all the way. Then, instead of enjoying long, expensive retirements, drawing on Social Security and siphoning resources away from the younger population, many of them die of lung cancer in their 50s.
This side of Logan's Run, no government could get away with killing off older people before they become a burden on the economy. But tobacco smoking gets people to remove themselves from the economy before they become liabilities. Sure, lung cancer is expensive, but it's less expensive than another 20 or 30 years of life, with a fair chance for some other expensive disease to come along anyway. (Look at Communist China, which doesn't do much to stop its subjects from smoking.)
In fact, the government doesn't even have to do the work (or incur the expense) of promoting smoking. Thanks to the free market, death merchants will do that for us. All the government has to do is lift the onerous bans on TV ads for smoking and similar regulations, and those who profit from lethal addictions will gleefully do the rest. We could make the switch in the name of "smaller government," "personal liberty ," and "property rights." (Libertarians will eat it up.)
It's unfortunate that lots of smokers are poor, the very people who can least afford to invest their funds into killing themselves. On the other hand, they're also the ones that the economy least minds losing to cancer and has to subsidize most in old age.
The same analysis doesn't work for booze. Alcohol (in the form of car accidents) often kills people when they're in their prime productive years, and it often takes other random people out at the same time.