Because their choices have consequences for others. You might not care about some health risk, but when you get sick, your family is going to be affected, your

Because their choices have consequences for others. You might not care about some health risk, but when you get sick, your family is going to be affected, your coworkers are going to be affected, and society has to pay for you to get well (by paying more for health insurance). And we're social animals. We care about one another. And caring sometimes means that we nudge people into a direction that makes them healthier. (I don't actually know if red meat is dangerous enough to justify a tax, but for the sake of argument, let's assume it is)