Spot the techie website commenters!
Here are some points against GM and they aren't all scientific issues:
Anti-GM activists != luddites. You can always shut down a factory when you discover that putting mercury into the rivers is a bad idea. It's very difficult to get rid of something which you've specifically introduced because it will be more successful than what was there before. Just ask the Australians about cane toads.
We already have enough food to feed the world. The reason people starve is down to politics and finance. If the issue isn't agricultural, the solution is unlikely to be agricultural.
Industrial-scale agriculture tends to increase the scale of production and tends to monoculture. Thriving eco-systems tend to be diverse. Assuming GM pest-resistance works, your pests may well be wiped out, just as effectively as using pesticides. The question becomes, have you accounted for wiping out that population (do any beneficial species need that pest), or do your accountants only look as far as the farmers? Could you end up with another pest because you've accidentally removed the food source for a predator which keeps it at bay? Again, ask the Australians how removing large quantities of conches has altered the crown-of-thornes population and its impact on the Great Barrier Reef.
GM can steamroll over other people's rights. GM is about ecosystems and not industry. Building a nuclear power plant next to a iphone factory does not affect the iphones. Planting GM crops next to a non-GM farm does affect the rights of those who don't want the "product" just as spraying pesticide from an aeroplane might affect people living in a house next to the field being sprayed.
Soil quality and food quality. You might be able to increase production but does the food nourish you? Those nutrients have to come from somewhere, mostly the ground. If you increase production (by GM means or simply intensive cultivation) you've got more food with fewer nutrients. In a lab you can compensate for this, but the question is whether the farmers in the real world will. Are you just increasing orange production by increasing the water content of the oranges? "Feeding the world" is a noble aim, but in the real world, money talks and it generally talks in terms of kilograms produced and sold, not in how healthy the people are. This isn't strictly a GM issue, but GM can increase the problem.
Point-of-sale qualities. Everyone like nice red tomotos, correct? (Somewhat) Wrong. People like ripe tomatos and the redness is an indicator. Now imagine if you you could make unripe tomatos look red using genes from a fish. You would sell more than the mix of half-green and red tomatos in the next stand, "because the market wants it." In fact, the market has been lied to.
Do we need more? "Helping the 3rd World" is fine, but where are these innovations used? Do we need more corn, wheat or rice in the West? While more gluten in the bread is great for fluffy bread which is a boon for jam-makers and dairy farmers (less substance per slice=>more slices->more jam & butter) overly cheap wheat (corn/soy) makes its way into all sorts of things where it doesn't need to be. It thickens soups, as it is cheaper than putting in more veg or meat - that sold-by-weight thing again. Pretend your allegic to corn, soy or gluten/wheat and check your supermarket products to see what is left that you could eat. Seriously, we (in the west) don't need this stuff. The developing world doesn't need us dumping it on the world market, subsidised by our taxes either.
Nutritionists generally say "pasture-to-plate" in as few stages as possible is the healthiest option, because industrial intervention generally turns out to be not for my good. I dislike the idea of industry getting in there and messing around with my food. The problem with GM is that it tends to spread. Again, it isn't just a GM problem. Cows being pumped full of hormones to keep them producing milk when it isn't natural for them to do so, has been going on for ages.
I had to laugh (and cry a little) at some popcorn imported from the US. I looked down the list of ingredients, popcorn, pecans, corn extract,.... then I looked at the ingredients list the importer had to stick on the can. Sugar, popcorn, pecans... Yes, the original suppliers had sweetened the product with a variety of processed sugars (mostly from grain crops) so that each one was less than the ingredient they wanted to appear first. I don't trust agribusiness to look out for my interests.
The agribusiness corporates are the ones most allied with GM (despite the fine ethics I'm sure the boffins have) because any automation or simplification of the processing reaps great rewards for them. I might trust Foxconn to make a phone for me, but seeing their attitude to costs, profit and employees, I certainly wouldn't trust them with my food.
The issues involved are far-removed from networking and computing. There are no firewalls in the fields. We have the science to mess with the genes of a plant. We don't always have the science to know what the effects of the modification will be globally or in the future and we don't have a fine-tuned legal system which could prevent consumers from being duped into buying something they don't want or which is harmful.
We can't even prevent the banks from doing things they shouldn't. What makes you think we have better control over the food industry?