We are all children sometimes, desperate to ignore the fact that what we want is not always what we need. Our adult selves retain a fascination with excess, falling off the wagons of healthy eating and safe units of alcohol and 10,000 steps a day with – for some – too great a frequency for comfort.

Weight-loss programmes falter not because we can’t educate our palates to enjoy grilled salmon and steamed green beans, but because sometimes – out of tiredness, or boredom, or excitement – we just really want a biscuit. I write as a woman who last week went to the very back of the kitchen cupboard in search of a small box of chocolate truffles I remembered having been given for Christmas. Reader, they turned out to be miniature bath bombs. It was a heartbreaking moment.

Happier was Jacob Rees-Mogg, who tweeted “the sweet smell of success” as he shared news of Boris Johnson’s proposal to review levies on products rich in sugar, fat and salt, widely reported as opening the leadership candidate’s war on a hated tax and, by extension, on the entire nanny state. But what does success really smell like if you’re JRM? One imagines a waft of Penhaligon’s Hammam Bouquet, with base notes of Gentleman’s Relish and a newly opened envelope from Coutts. The holes in Johnson’s whiz-bang new vote-winner soon began to appear: a review of the effectiveness of levies on the manufacture of high-sugar soft drinks is already in progress; and contrary to one of his central arguments – that such a tax is simply a way of further impoverishing consumers – evidence suggests that the makers of such drinks have reduced their sugar content rather than stumping up for the levy and passing the cost on to the poor old public.

A Conservative approach will seek to persuade us that any restriction on what we do is an assault on our freedom

But that was never the point of the “announcement”. Rather, it allowed Johnson to deploy the phrase “sin taxes”, and to suggest that his primary purpose in getting rid of them will be to help those on lower incomes. It’s a strategy so transparent that to parse it is almost to feel one’s synapses shutting up shop for the day. Because nobody can seriously believe that to consume sugar – whether in a stodgy jam doughnut or a glass of Château Lafite – is a moral or ethical failing. A fondness for Haribo does not indicate a bad character, just as to dine on kale and pumpkin seeds does not turn one into Mother Teresa.

There is a far more mundane rationale: the medical experts are increasingly of the view that a diet containing too much sugar, salt and fat is no good for us; that it will contribute to making us heavier than we ought to be and unhealthier than we need; and that food and drink manufacturers can help us out by not pumping our grub full of them.

This is not an argument that sits well with those keen to sell a dream of liberation from the tentacles of the state, for whom the idea of personal control over one’s consumer choices must be neatly conflated with control over one’s social and political circumstances. For no matter if you have to wait three weeks to see your GP, or find a way to mind your children when their school has had to shorten its opening hours, or if your house is uninsurable because of climate-related coastal erosion; you are free to drink as much fizzy pop as you like, and at a price that suits.

It is not how a sane society should live. Folded into such a brave campaign to let us drink Vimto for breakfast, lunch and dinner should we choose was the promise of more of this sort of thing come 31 October, and “a historic opportunity to change the way politics is done in this country”. Fill your buckets and your bellies with as many sweets as you like, trick or treaters!

But we don’t have to enshrine these instances when we act against our best interests – not from moral weakness but from a sporadic inability to regulate our perfectly natural appetites and desires into the social fabric. There, we have scope to take the longer view; to plan how to live as well and as happily as we can, for as long as we can, limiting our exposure to avoidable dangers.

A Conservative libertarian approach will seek to persuade us that any restriction on what we do – and more crucially, on what we buy – is an assault on our freedom, an affront to the destiny we should be enjoying were it not for busybodies. How distasteful it is to show that your concern for the poor extends as far as enabling them to pile their shopping trolleys high but short of providing them with adequate healthcare, education and housing. Don’t fall for it: in this case, a spoonful of sugar will definitively not help the medicine go down.

• Alex Clark writes for the Guardian and the Observer