It tallies with Cameron's right-wing libertarian small-government ideas, but it actually owes more to his time spent on the Home Affairs Select Committe in 2002 when, like anyone else examining the evidence objectively, he came to see that prohibition has none of the benefits its proponents claim and causes huge damage.
Cameron's stance beats his colleague Alan Duncan who, as I've said before, argued for legalisation until he got a frontbench post then he had a new edition of his book revised to omit his stated support for the idea and has voted for prohibiton laws ever since.
Writing in The Independent, Johann Hari picks up on Cameron's position and eloquently makes the case for legalisation that longer-term Badgerers will be familiar with as one of my ongoing rant-points.
He also includes a horrifying news item that had gone right under my radar.
As if on cue, the Government is doing something this week that illustrates Cameron's arguments about the weird evidence-free nature of the war on drugs in blood-red Technicolor.
Right now, 2,500 British troops are about to be despatched to trash one of the only cash-crops in the poorest country in the world - and they are going to kill anybody who fights back.
The 16th Air Assault Brigade is flying into the Afghan province of Helmand, where they have orders to "secure" the fields of dirt-poor farmers growing opium and destroy them. British Army commanders briefed a newspaper that they expect the farmers to stage an uprising when their livelihoods are wrecked and they face starvation.
So - strike up "Land of Hope and Glory" - we will then have British forces firing on some of the poorest people on earth after destroying their only source of income. It's as if the Government was dealing with binge-drinking by sending Swat teams into Oddbins and despatching the SAS to commit massacres in rum distilleries in Jamaica.
Although this "operation" might seem very distant from domestic concerns, it is an illustration of the strategy carried out back home in one crucial respect. Whenever politicians order "crackdowns" like this, they have invariably been warned by their experts that it is a waste of time. Tony Blair's Strategy Unit warned him in 2003 that targeting drug-supplying countries squanders blood and money. "Drug crop eradication appears not to limit illicit crops in the long term," it explained dryly.