It's strange that at this week's World Economic Forum the designated voice of the world's poor has been Bill Gates, who has pledged £478m to the Global Fund to fight Aids, Tuberculosis and Malaria, telling Davos that the world economic crisis was no excuse for cutting aid.

It reminds me of that dark hour when Al Gore, despite being a shareholder in Occidental Petroleum, was the voice of climate change action – because Gates does not speak with the voice of the world's poor, of course, but with the voice of its rich. It's a loud voice, but the model of development it proclaims is the wrong one because philanthropy is the enemy of justice.

Am I saying that philanthropy has never done good? No, it has achieved many wonderful things. Would I rather people didn't have polio vaccines than get them from a plutocrat? No, give them the vaccines. But beware the havoc that power without oversight and democratic control can wreak.

The biotech agriculture that Lord Sainsbury was unable to push through democratically he can now implement unilaterally, through his Gatsby Foundation. We are told that Gatsby's biotech project aims to provide food security for the global south. But if you listen to southern groups such as the Karnataka State Farmers of India, food security is precisely the reason they campaign against GM, because biotech crops are monocrops which are more vulnerable to disease and so need lashings of petrochemical pesticides, insecticides and fungicides – none of them cheap – and whose ruinous costs will rise with the price of oil, bankrupting small family farms first. Crop diseases mutate, meanwhile, and all the chemical inputs in the world can't stop disease wiping out whole harvests of genetically engineered single strands.

Both the Gatsby and the Bill and Melinda Gates foundations are keen to get deeper into agriculture, especially in Africa. But top-down nostrums for the rural poor don't end well. The list of autocratic hubris in pseudo-scientific farming is long and spectacularly calamitous. It runs from Tsar Alexander I's model village colonies in 1820s Novgorod to 1920s Hollywood film producer Hickman Price, who, as Simon Schama brilliantly describes in The American Future, "bought 54 square miles of land to show the little people how it was really done, [and] used 25 combines all painted glittery silver". His fleet of tractors were kept working day and night, and the upshot of such sod-busting was the great plains dustbowl. But there's no stopping a plutocratic philanthropist in a hurry.

And then there is the vexed question of whether these billions are really the billionaires' to give away in the first place. When Microsoft was on its board, the American Electronics Association, the AeA, challenged European Union proposals for a ban on toxic components and for the use of a minimum 5% recycled plastic in the manufacture of electronic goods.

AeA took the EU to the World Trade Organisation on a charge of erecting artificial trade barriers. (And according to the American NGO Public Citizen, "made the astounding claim that there is no evidence that heavy metals, like lead, pose a threat to human health or the environment".)

Now, the EU is big enough and ugly enough to have fought and won the case. But many an African country lacks the war chest for such a fight, and so will end up paying for the healthcare of those exposed to leaky old PCs' cadmium, chromium or mercury, instead of embarking on, let's say, a nationwide anti-malaria strategy. Bill Gates himself may not indeed have known about what the AeA was doing on Microsoft's behalf, but the fact remains that if a philanthropist's money comes from externalising corporate costs to taxpayers, and that if Microsoft is listed for its own tax purposes as a partly Puerto Rican and Singaporean company, then the real philanthropists behind these glittering foundations might be a sight more ragged-trousered than Bill and Melinda.

Free marketeers will spring to the defence of billionaire philanthropists with a remark like: "Oh, so you'd rather they spent all their money selfishly on golf courses and mansions, would you?" To which I reply: "Oh, you mean that trickle-down doesn't work, after all?" But the point is that the poor are not begging us for charity, they are demanding justice. And when, on the occasion of his birthday, a sultan or emperor reprieved one thousand prisoners sentenced to death, no one ever called those pardons justice. Nor is it justice when a plutocrat decides to reprieve untold thousands from malaria. Human beings should not have to depend upon a rich man's whim for the right to life.