Genetically modified crops are excellent technology. If Britain and the world had agricultural policies that truly were designed for the benefit of humankind - to feed everybody well, provide employment and look after the environment - they might be useful in many ways; and this weeks Monsanto decision to give up on GM wheat might be regrettable.

But we have no such policy. Instead we have a mantra embraced by the World Bank, the IMF, the World Trade Organisation, and the US and British governments: "Agriculture is a business like any other." This dogma is leading the world in totally the wrong directions - and within it, GM crops have become key players.

For agriculture qua business must seek to maximise profit. So it must maximise turnover and output. Scientists and politicians claim this must be good - for there still are famines, and the world population is set to increase by 50% to around 9 billion by 2050.

But the recent famines have rarely resulted from inability to produce food. Almost always you find civil war in the background, corruption, or - as in the Ireland of the 1840s or recently in Argentina - starvation in the midst of plenteous crops that are earmarked for export. In the short term, more production leads to glut - and so world prices for coffee have dropped by nearly 70% in the past five years. The world population is indeed rising but (says the UN) it will stabilise by 2050 and no frenetic increase in food is required. Besides, by then the worlds livestock will be consuming enough grain to feed 4 billion people. If we ate less meat we could feed ourselves easily. All thats needed is traditional cuisines, which use meat sparingly. But the business dogma requires ever more livestock because that is where the profit lies.

Agriculture qua business must then strive to minimise costs. This is dangerous: cheap cattle-feed (made from bits of other cattle) is what caused BSE. Worse: cutting costs means cutting labour, which traditionally is the biggest input. After the second world war, about 20% of Britains workforce was on the land, while now (like the US) we are down to a little over 1%. The foot-and-mouth epidemic arose from too little care - farming run on a wing and a prayer. But thats business.

In Britain, the rundown of the agrarian workforce is foul, but not quite disastrous. We are rich and have alternatives. But in the developing world, 60% of people work on the land. In India, that is 600 million. Commercial forces worldwide have been urging India to industrialise its farming as Britain has done. This would increase yields and bring down costs - but would also put at least 500 million out of work. The envisaged alternatives fall short of what would be required by orders of magnitude. IT, Indias great success, employs barely 100,000. The world as a whole needs to remain primarily agrarian - but if agriculture is just a business, then the fewer on the land, the better.

And if the mantra was applied rigorously, then Britain would get rid of farming altogether. There is nothing we can grow here that could not be grown more cheaply elsewhere. Indeed, beneath the pieties of successive secretaries of state for the past 30 years, the question is implicit: why dont we get shot of agriculture, just as we got shot of mining? Indeed it seems that British agriculture survives (just) only because it is conspicuous and run by influential people, while mining was done out of sight by, well, miners. But farming continues to embarrass British governments. It runs entirely against their economic logic.

So what is the actual role of GM crops as things are? They can increase yield. They can help to reduce labour even more. Pest-resistant GM crops make mass uniform production possible. This may improve on the now "conventional" dousing in industrial chemicals, but is nothing like as good in principle as traditional husbandry, in which pests are contained by mixed cropping and rotation. So high-tech is not used to abet good husbandry but to make bad practice possible. That is more profitable.

More broadly, the present world trend on all fronts is to transfer power from the many to the few. If traditional people grow their own traditional crops they have autonomy. We might reasonably feel that this is desirable, but business must seek its share of the action: "market opportunities". If the world as a whole embraces GM crops, then all agriculture will be controlled by a few high-tech companies and the governments to which they are loosely answerable. All hope of autonomy is wiped out at a stroke. This is already happening.

A radical rethink is needed in all agriculture: social, economic, political, scientific, technical. When the thinking has been done, the world may find roles for GM crops. Until then, they must be resisted.

Colin Tudge is author of So Shall We Reap, on the state of world food.