Agriculture is probably a good example of the process at work.
You're right that most GM crops have been modified for pesticide resistance. But there is nothing wrong with that per se. They actually reduce pesticide use, by allowing farmers to spray a broad spectrum herbicide selectively, after their crop has emerged, rather than at seeding. And they've made it easier for farmers to shift to soil conservation farming techniques like zero-till, which reduce soil erosion and fossil fuel use. In Canada, the number of farmers using zero- or minimal-till techniques on the prairies has tripled since the introduction of Roundup-ready canola, for example.
That's where I think the left has gone astray. By concentrating its attacks on the technology itself, and promoting unjustified fears about the safety and environmental effects of GM crops, it has missed the real target: corporate control of the technology.
Take the Percy Schmeiser case you allude to. Schmeiser didn't end up with a few Roundup Ready plants in his fields. The courts found that he had deliberately propagated and sown an entire crop of Roundup Ready canola. Why? Because it was better than the non-GM seed varieties he could have planted. But Schmeiser, instead of playing dumb, could have made an important argument: Monsanto requires farmers who buy Roundup Ready seed to use Roundup, and not generic glyphosate, as part of their licensing agreement, which is clearly counter-competitive.
Even more importantly, the attacks on GM technology have muddied the international debate about intellectual property rights. Companies like Monsanto have won patent protection for many of the most valuable genetic sequences. Which is incredible in itself. But they are only interested in using them in those crops common in North America, where farmers have the money to buy the seed. So in Africa, for example, where more than half the annual crop is lost to insect pests and weeds, public researchers have been prevented from using GM technology to produce Roundup-ready cassava, say.
The combination of broader patent protection and the steep decline in public spending on agriculture research has gone, I think, largely unnoticed. So far the GM debate has focused on safety, instead. The real debate--and the key political question--is whether GM crops will be developed by public institutions or by private companies.