There is Hayek’s point, that the central planner never can quite measure the world accurately enough to be able to plan things properly. We then go on to insist that even if we’re going to ignore that - because some things really do require management even if it cannot be done perfectly accurately - then we do have to devote a certain effort to trying to measure matters as well as we can.

For example, we insist that all measures of the wealth distribution are wrong because they, quite deliberately and openly, ignore the effect upon that wealth distribution of all the things government currently does to change it. We continually point to the manner in which estimates of climate change damage are vastly too high as they entirely ignore what has already been done to avoid those worst future projections.

We seem to have another example here with the Body Mass Index:

Growing numbers of women and men in England with eating disorders are being denied support because they are not considered to be thin enough to warrant it, a leading psychiatrist and other experts have warned in a briefing shared with ministers.

Against the backdrop of a fourfold rise in people admitted to hospital with eating disorders during the Covid pandemic, doctors said body mass index (BMI) was too often used as a blunt measure to decide whether someone should get treatment.

In some cases, women have not received an eating disorder diagnosis despite their periods stopping due to overexercising or restrictive eating.

BMI uses height and weight to calculate a healthy weight score. A normal body weight is considered to be between 18.5 and 24.9, and some doctors consider anything below this a signifier of an eating disorder.

The point here being that at least some people considered “normal” by that BMI are quite clearly too thin to be healthy.

It’s also possible to point out that those considered “overweight” and shading into “obese” - but not “morbidly obese” - by that very same BMI measure have better health outcomes. More years of life, more years of pain and sickness free life.

It would appear that we’ve pegged the definition of normal too low - or perhaps the definition of desirable.

All of which does play to our own insistence on counting things right. Once we do so solutions to the perceived problems become much easier. A more equal wealth distribution is achieved by counting what we already do to gain such. Climate change is at least in part beaten by how we’ve already made wind and solar power so much cheaper than they were. Britain’s obesity crisis can be lifted simply by shifting our definitions.

The current definition of “normal” weight is unhelpfully, often enough dangerously so, thin. So, rebase to normal being what is currently considered overweight, that BMI which is, in fact, healthier. At wihch point, largely enough, we’re done. No need to eviscerate commercial freedoms and civil liberties by banning foodstuffs, or advertisements for them, or supermarket placings. Unless, of course, the power to do those things is the point of the scares about BMI and obesity in the first place.