Today I was on BBC World talking about obesity. My opposite number Tam Fry pointed out that the obese cost the rest of us while they are alive through their use of the NHS and other state services. I pointed out that they don't totalled up over the lifetime because the obese die earlier and take much less out in pensions and end-of-life care.

In saying this I was trying to make the point that this doesn't mean we shouldn't care about obesity, or that it's (heaven forbid!) a good thing because they cost the rest of us less. Are people so obsessed with the government's balance sheet that pointing out the obese cost the government less by dying earlier seems equivalent to saying I want them to die earlier?

My point was that most of the costs of obesity are to the individual, not to society. There is no harm principle argument here that we should intervene into their lives because they are hurting others. The case for intervening into the lives of the obese would be to make them better off, because say, obesity shortens their lives, makes them more likely to get diabetes, or makes them less happy.

Now I don't think there's never a case for paternalistic intervention (we can all think of crazy thought experiments) but I do think we should be very careful before we decide we can run someone's life for them. That's because usually the government gets things wrong when it tries to plan on other people's behalves.

Most people would not like to live in a society where people are not at least in some cases free to take the steps that lead to obesity—even if overall they'd prefer there were fewer obese people. Most people would find it rather chilling to have a society where the diets and exercise regimes of the obese were centrally managed and rigidly enforced.

By contrast, the Mexican 'squats for bus tickets' scheme, though very likely to be ineffectual, is probably not such a bad idea.