After seeing a documentary on the plight of Mexican corn farmers, I don't like them.
There are a few specific issues I have with GMOs. First off, one of the most common forms of genetic manipulation is to genetically modify crop seeds so that they are resistant to herbicides. An example of this is Monsanto's infamous "Roundup Ready" soy and corn. The idea is that by making the crop resistant to the herbicide, pesticides can be sprayed with impunity... and although all other plants will die, the main crop will live. This is great for large scale farming, just plant your seeds, water, and spray with pesticides. The problem is that this leads to weeds that start to develop a resistance to the herbicide, and thus greater and greater amounts of pesticide get sprayed onto our foods.
Another problem are "Bt" crops that have been genetically modified to produce a toxin that kills known parasites. Not sure if there is any documentation on the effects in humans, but this has created some unintended problems with overall ecology. In addition to killing the pests, there has been some concern that non-pest pollinator insects have also been adversely affected by the toxin. Another tangent of this is that the pest-killing features of the Bt crops change the mix of insects in a field. By killing the "pest" insects, the relative ecological balance is disrupted... there are other insects whose populations might increase or decrease as a result of a missing component in the natural ecosystem. None of this might seem striking if these GMO fields were isolated plots of land... but, not only are GMOs being used quite readily all across many countries, we are now realizing that its next to impossible to halt the spread of GMO pollens from entering surrounding non-GMO ecosystems. We may end up with GMO elements weaving their way into ALL plant life... at which point these minor sounding issues can develop into full blown ecological crises, where entire species of insects may go extinct.... and as we all know, nature is interrelated, and playing games with large scale ecosystems that encompass most all of our arable farmland might have disastrous and irreversible consequences.
Another problem I have with them is that the entire GMO industry is migrating to one where the intellectual property component of their genetic code will be maximized for profit. There are dark rumors that GMO seed could potentially be manipulated so that it ONLY grows and produces food yield if a proprietary kind of fertilizer is used. In other words, if you want the benefits of the high yielding and profit maximizing seed from GMO company A, you also need to buy the fertilizer from GMO company A... or else the plants are programmed never to bear fruit, as an example. This may seem trivial, but if the purchased seed gets cross-pollinated with indigenous seed stock, you could create a situation where ALL of the seeds require the proprietary fertilizer.... and by not buying the Company A seed and Company A fertilizer, you might not just be forgoing the higher yields that Company A seeds provide, you might be putting yourself in a situation where you will get NO YIELD unless you use the Company A seeds. This could put vast swathes of the world's farmers at the mercy of Big GMO Agrobusiness for their daily livelihoods... when, in past days, they could just have maintained their own seed stock. Fear of this is part of what drove the creation of the Doomsday Seed Vault.
So... there are a lot of unknowns about GMOs. And, its not necessarily the effect on humans from eating them, but, I don't think the long term effects of inserting human manipulated genetic material into plant life that can spread uncontrollably all throughout the world have been thought out very well.
