I wager his radical change had something to do with a fairly large sum of money.
There's an argument that GMO's have abnormal properties which screw about with people's internal chemistry, even tampering with their DNA to an extent, but that's on the extreme side of the debate, and I certainly have my doubts. The less debatable issue is that companies like Monsanto are making a concerted effort to turn agriculture on a global scale into corporate capital.
There's no big mystery surrounding GMO's really, and the science isn't always quite as complex as it sounds, albeit sometimes it's rather more. In the eighties if I remember correctly a patent was filed for an engineered bacteria that consumes oil. The patent office turned them down on the basis lifeforms are explicitly not available for patent. At that time only isolated biological components could be patented, things like adrenaline, for example. Those seeking the patent (probably Monsanto, but I'm not entirely sure.) appealed to the legislature, and using diagrams and descriptions more akin to chemicals than bacteria, and espousing the environmental need for such a product, convinced congress to pass a law allowing for genetically modified organisms to be patented.
Ever since GMO's have expanded well beyond the realm of bacteria, producing such odd but perhaps beneficial organisms as Mosquitos that are malaria resistant. I'd even heard there'd been contemplations of Mosquitos which could carry a malaria vaccine.
One of the less complex but far more profitable uses of GMO's is to produce specific 'brands' of corn/wheat/rice, ect, which can be easily identified when tested. The companies which produce these 'name brand' seeds, primarily Monsanto, then advertise the great benefits of these seeds, how the resulting plants might be bigger/have greater yield/drain the soil less/prove more hardy/contain pest repellants 'naturally', just as one might any other product. Also just as with any other product, sometimes the claims seem to be embellishments, and so things don't work out quite as hoped. Monsanto very often contracts out this seed, so just like that pesky cell-phone contract that doesn't work out but can't be got rid of for a year or two, farmers find themselves bound to these seeds for years at a time. In the Indian cotton-belt for example, Monsanto contracted out large amounts of the cottonseed on the promise of a better plant. It didn't pan out, yields decreased, and suicide rates among the farming community apparently spiked considerably as farmers were locked in their contracts which couldn't produce living wages, and sank them into crushing debt.The contacts also forbid farmers from saving the seeds their plants produce, obligating the farmers to buy new seed each new crop-season where non-perennials are concerned, or even I've heard in the case of some perennials, requiring farmers to raze their plants after harvest. I can't confirm that last point, though.
There's also been allegations Monsanto has prosecuted farmers when their crops have been inseminated by the pollen from Monsanto plants for patent violation, though Monsanto states this accusation was only a single case, and it was proven false in the Supreme Court of Canada. This particular case was apparently featured in the documentary Food Inc.
Theres a portion of the Monsanto statement in regards to that case which I found rather interesting however:
If a suspected instance of a farmer violating our technology agreements or patent rights is reported to us, we do not automatically assume a farmer has intentionally acted in an unethical or criminal manner. The burden of proof is not on the farmer. Instead, the burden of proof is on Monsanto to investigate the legitimacy of these claims and to resolve the issue as quickly and fairly as possible, which usually does not lead to litigation.
So they directly state they take it upon themselves to investigate issues of patent violation, meaning that if they suspect you're using their seed illegally, they'll show up at your farm to run tests/ask questions. Whether they do so in all humility and politeness or there are levels of intimidation involved, it seems to me a rather overly authoritative stance for a seed-vendor to take.
Monsanto's exceedingly successful efforts aren't secret by any stretch, they're publicly documented. Whether the spread of their products, which is undeniably occurring and sometimes the stated intention, into the rest of the environment is having a negative influence on natural ecosystems, or if genetically modified food has a negative influence on health is up for debate, though the big money, figuratively and literally, is on Monsanto in that issue. Still, they aren't at all the world-saving products Monsanto advertises them as, and the more clearly legitimate concerns are with what corporate control of the global agriculture system would mean for people and their livelihood, and there's little to no question that's Monsanto's dream.
Indeed food could be described as a commodity, but agriculture is the staple food-source of most human beings on the planet. Corporate interests already have control over a vast percentage of food distribution planet wide, and it hasn't had an overly positive influence on starvation figures. Corporate monopoly of agriculture from the soil up isn't likely to lead to the utopian world of surplus Monsanto's PR department would have us believe, given maximum profit is the mandated goal.
It's not a secret conspiracy, but it is entirely unprecedented, and the socio-economic implications, including the influence it could have on starvation in impoverished nations, are ominous, the environmental/health debates aside.