GMOs can be safe, they can be unsafe. For instance, if you inserted a gene into a potato to produce poisonous cyanide compounds that would be unsafe. Engineering a rice variety to produce Vitamin A precursors, however, is not likely to be unsafe on a basic scientific level and once the crop has been tested and retested for toxicity and other concerns it is simply not plausible that it would be dangerous.

Other intentions of GMOs can be, for instance, to produce an organism which is naturally resistant to pests or which is better able to grow in a variety of climates. With regards to pest resistance the toxicity of the compound would, of course, have to be tested first - but artificial pesticides are regularly sprayed on crops anyway so I do not see how it is different.

With regards to increased proliferation or better adaptation to more climates, the fear that they will somehow destroy the ecosystem is quite unfounded - if a plant which was slightly better adapted could do this evolution would have assured mutual destruction by know already. Remember that modern varieties of crop plants are probably not well suited to growth outside of human cultivation, being bread to human needs which may be maladaptive in the wild. GMOs are no more capable of taking over the world than their wild type counterparts I assure you - we are years and years away from being able to design something so effectively!

Look at what the basic science of genetic modification is - inserting a known gene or known series of genes into an organisms code under the control of specific gene switches in order to get a desired phenotype. Its not that scary really, an additional gene or an additional few genes added to what is no doubt already thousands. It is merely an accelerated and highly specific form of artificial selection which has been going on for centuries. The exact function of the genes being inserted will no doubt have been ascertained precisely before getting anywhere near the stage of producing a GMO. The only potential risk I can think of is unexpected interactions between metabolites in other biochemical pathways - but this would be picked up on pre release testing and possibly even in silico modelling, and thus can be easily managed.

The fear over GMOs is quite out of control, for instance I have in the past worked with GMOs in a lab setting. This were genetically modified fruit flies (which had the reporter gene Lac-Z added next to genes of interest in order to permit visualisation of gene expression) and Chinese hamster ovary cells which had the cannabinoid receptor artificially added to their repertoire. With both the control were laughably excessive, the fruit flies are no different than their wild type counterparts in terms of any threat of danger and the CHO cells like to die even when good care is taken of them in highly controlled conditions (trust me, they wouldn't last a day if they got out of the lab). Yet still, we had to put up with the highest level restrictions and procedures when working with these in order to absolutely rule out environmental contamination - including intrusive inspections by government staff.

One of the big problems (frequently raised by objectors, pretty much ignored by supporters) is that the purpose of GMOs is so Monsanto can have a plant they own, rather than because the plant is a good idea per se. This may not be a great idea.

I agree that a lot of common worries about GMOs are just plain silly. The kind of people who worry about GMOs because "we don't understand what we're changing" are also the kind of people who are more likely to buy 100% natural Tibetan herbal tea even though the same concerns apply (rare exotic plants are more likely to contain rare chemicals whose side-effects are not well studied and understood).

Still, there are some reasonable concerns about GMOs -

• their use may reduce biodiversity if one "optimal" crop is used everywhere (but the same applies to conventional breeding and optimization of crops);

• "terminator" seeds (plants that don't regrow and must be rebought) and copyrighting of some plants might suck, but I don't know enough about economics to tell how much if at all (though I could fall back on either "yay science" or "boo corporations" and come up with a post-hoc justification)

• Making plants more resistant to insecticides so the farmers can spray even stronger insecticides doesn't seem that great, but again I don't know enough to tell the good from the bad.

Corn has been bred to grow six feet tall, among other things. What's a little GMO in comparison?

According to the World Health Organization:

GM foods currently available on the international market have passed risk assessments and are not likely to present risks for human health. In addition, no effects on human health have been shown as a result of the consumption of such foods by the general population in the countries where they have been approved. Continuous use of risk assessments based on the Codex principles and, where appropriate, including post market monitoring, should form the basis for evaluating the safety of GM foods.

The reasoning most laypersons employ when thinking about GMOs is totally broken. For example, people worry about whether GMOs are less nutritious or unhealthy in some other sense. But there is no reason to think GMOs as a category would be skewed in any one direction, since any given plant might have different modified genes. It needs to be looked at in a case by case basis. Furthermore, GMOs aren't being developed in some Wild West free market. They are among the most carefully regulated substances you can ingest.

ETA: As for the concern about self-replication, that shouldn't be too serious of a problem. Domesticated organisms are optimized for thriving under human care, and pretty much every domesticated plant and animal does poorly in the wild.

I'm concerned about allergies-- for example, fish genes being put into tomatoes for cold resistance, though I just found out that it was never commercially produced. Some people can literally die from eating a small amount of fish, and I don't know whether any of the dangerous fish proteins were in the tomatoes.

Even if you're talking about less drastic engineering, moving genes around could make life a lot harder for people who need to know which foods are safe for them.

I am more worried about the follow-on effects than GMOs per se, for instance when crops are modified to be immune to herbicide farmers will no longer have any incentive to moderate their usage.

That would be a topic I changed opinions on twice. Currently I am convinced there is a potential for danger that is noteworthy. The effects nutrition has on the human body are not actually understood well enough yet, and the genetic tinkering is also not that well understood. (As a IT person I intuitively want the source code to feel safe. Maybe that is asking too much.)

There is no reason to be deeply afraid as compared to other bad influences on your health, or to go about burning down fields. Just avoid the stuff if possible. And re:check every few years if there are new facts to consider.

The technology should be further used and researched. So far there is not too much real long term data - as with many other technologies. A General problem with highly unified systems is a possibility for a single point of failure that hurts a noteworthy part of the population at once. Here the risk of damage to the human body that only shows up after decades, and then takes effect whole populations at once.

The risks that GMOs pose to us are more likely to come from the companies that grow them. The corn they grow here in the states is used for everything from plastics to soda and new uses are undoubtedly being uncovered all the time. Personally, I don't like corn THAT much. A corn takeover is not much of a doomsday scenario.

There are some environmental issues that arise from supporting corn crops. Some crops 'give back' to the soil. Corn is not one of them.

[WARNING: UNINFORMED OPINION FOLLOWS]

Another, keener health risk concerns something I heard about The Omnivore's Dilemma. The problem with some GM foods I hear is that they are far lower in nutritional value than other foods.