Illustration by David Foldvari.

For as long as I can remember, there have been sweets next to the tills at supermarkets. It was my first experience of retail guile. "Never mind that trolley full of boring stuff you need, like bleach and runner beans and bin bags, why not buy something you want?!" the displays seemed to be saying. "Come on, let go a little, relax your bottom on to the comfortable surface of this lovely slippery slope."

Those were the terms in which my parents, keen for me to grow up well-grounded in cynicism, explained things to me. Chocolate and crisps were all very well, but to buy them by the checkout, on an impulse, was falling into a trap. Instead, I was taught the pleasure of watching other people fall into it and feeling smug. The fact that the sensation of smugness was more pleasurable to me than that of salt or sugar tells you all you need to know about the kind of monster who comes to prominence in modern Britain.

So I was alarmed to hear, last week, that this pleasure may soon be denied me. Jane Ellison, the new public health minister, identified the placing of delicious crap near tills as "an area for action under the Responsibility Deal" and said: "Parents have indicated that positioning of sweets at checkouts can increase pestering to purchase by their children." This contrasts strongly with the comments of her predecessor, Anna Soubry, who said: "There's nothing wrong with sweets" and "I just said no to my children." Her confrontational approach caught the prime minister's eye and she's since been moved to the Ministry of Defence.

However, when it comes to tempting checkout areas, Cameron is in Ellison's camp. In 2006, still fresh with zeal to change the world, he condemned the disgraceful absence of fresh fruit from newsagents. "Try and buy a newspaper at the train station and, as you queue to pay, you're surrounded, you're inundated by cut-price offers for giant chocolate bars," he said. "As Britain faces an obesity crisis, why does WH Smith's promote half-price Chocolate Oranges at its checkouts instead of real oranges?"

That was seven years ago so I assume someone has given him an answer. But just in case, I'll have a go. Well, you see, WH Smith is a newsagent's chain so it's really not set up to deal with fresh fruit. I don't know whether Mr Cameron imagined it diversifying into oranges alone, or providing a whole fruit range, but either course presents logistical difficulties and wouldn't, in my view, provide sufficient revenue to compensate for stopping selling sweets and chocolate, or hiding them at the back with the A-Zs and toner cartridges.

But what about his obesity point? Well, you see, WH Smith is a newsagent's chain and has no responsibility for public health. Its management answers to shareholders who are unlikely to view a reduction of national fatness as mitigation of a collapse in confectionery sales. That's what happens with a free market – I'm surprised he's got a problem with it.

Suspicious though I am of supermarket chains, I do feel it's unreasonable of the government to expect shops not to arrange their wares to best advantage. It's like saying ice-cream vans mustn't turn up at parks on sunny days because it's unfairly tempting, and should only be allowed during thunderstorms – and only then selling to those who have thrice refused the offer of some lentil broth.

Special rules apply to tobacco and alcohol, but do we really want to extend similar exceptions to everything else that might do us harm? In moderation, almost anything is fine and, out of all moderation, absolutely nothing is – you can be crushed under a ton of vitamin tablets, ingest so much water you drown, eat so many sprouts you have to get a Corgi certificate.

How are we to categorise which are the officially unhealthy foods, the shameful merchandise that needs to be separated out like booze and fags? Carrots are definitely good and Haribo definitely isn't. Easy. Crisps bad, eggs good (they've got the good sort of cholesterol this month). Cheese – bad? But what about all the calcium? And kids don't tend to ask for some Shropshire Blue in the way they'll latch on to a Fanta. But what about cheese string?

Nuts – they're good, they can go by the tills. Then again, what about salted nuts? Let's keep them away. Then, what about slightly salted nuts? As soon as the category is defined, the search will be on for the most unhealthy food that doesn't fall into it, which can then be arranged temptingly round the checkouts.

I'm being naive. It won't be done like that – this is the "big society" after all. As a Department of Health spokesman said: "We have been clear that legislation is not necessary and that the voluntary approach through the Responsibility Deal is working." So there'll be no new rules and the supermarkets will act of their own accord out of their sincere wish to do good. And by "out of their sincere wish to do good", I mean "to head off the threat of legislation while their lobbyists get to work on ministers".

The only virtue of which public limited companies are capable, in my view, is honesty. We can sometimes make them tell the truth. We can make them publish accurate accounts, use transparent employment practices and hold public shareholder meetings. When corporations cannot lie, the world is a better place. Yet, under this policy, we are requiring them to lie.

Employees and management at supermarkets may share Jane Ellison's concerns about public health but the institutions themselves – these vast organisations, owned by thousands of shareholders and shareholding institutions – are incorporated purely to make a profit. They therefore wish to sell as many sweets, as much of anything, as possible. They do not – they cannot – want customers to restrict their purchases to what is good for them and, by harassing these companies to say they do, we force them to lie.

The world is not safe and we don't make it safer by pretending it is. People should expect naked commercialism from retailers – we all need to get used to it and learn to resist it. It's as honest as any kind of predation. By forcing supermarkets to lie about their aims, we inhibit the development of public cynicism and, like an over-relied-upon satnav, lure people into believing that it is safe to proceed without vigilance.