> Actually, all those things you listed _decrease_ lifetime medical costs. From a purely economic sense, people who drink, smoke, and eat junk food are _ideal_. They're reasonably healthy during their most productive years, and then mortality rate spikes just before retirement (a time when most people are least productive).
Actually, the numbers don't back that up. A person doesn't get diabetes and die the next day with no medical costs. A smoker doesn't get lung cancer and die tomorrow. They might not live as long, but their medical costs are higher the entire time, and the older they get, the higher the costs become. Eating poorly is especially costly because it doesn't kill people quickly, but causes significant health problems.
> So if the logic is that we tax things based solely on economic externalities, then we should encourage drinking, smoking, and obesity. We should subsidize all those activities.
No, the logic is that we provide healthcare to everybody so that they can have longer, healthier lives. Makes no sense to waste money on the people actively working against that goal, so if smokers/drinkers/fatties want to take part then they need to cover the extra costs they've created for themselves.