The USDA is currently accepting public comments on the issue of allowing a Genetically Modified Alfalfa plant developed by Monsanto, which could, by the USDA's own research, infect organic alfalfa farms, potentially causing them to lose their 'organic' labeling. Needless to say, many people are upset about it, not the least of which are the people at Food Democracy NOW!, who want your comments. Now, this product has made it past USDA environmental review, that, in theory, shows that the environmental impact of this GMO crop will fall within acceptable levels, however those are defined.
FDN is calling this something that 'threatens the very fabric of the organic industry.' Now, I think that battle was lost years ago, when Organic was defined in such a way that the biggest players in Organic are companies like Kraft and Heinz, but the real issue here, in my opinion, is the danger of these GMO crops. Not that they'll cause health issues with those who consume them, but rather the danger to the ecosystem, particularly when you look at the docket and realize that this GMO is only meant to be herbicide-resistant. A so-called 'Roundup Ready' crop.
It is the nature of agriculture to support the cultivation of certain plants at the cost of others, however, with these 'roundup ready' crops, it encourages wholesale dumping of these chemical plant-killers in manners that don't necessarily control the application of the chemical very well, which can kill plenty of plant life that is found in areas external of the GMO crop, further reducing plant diversity (and most likely insect/animal diversity by extension) in those areas. Plus, since the plant has been modified to be difficult to kill, when it does spread to non-GMO versions, it becomes impossible to separate the GMO version from the non-GMO version, further reducing biodiversity. It is this cross-breeding between GMO and non-GMO life, and the fact that the non-GMO life is almost guaranteed to be the dominant form over time, that worries many ecologists.
The monoculture present in modern agriculture is already worrying, but has, until recently, still been based on traditional selection, with change in an organism happening slowly over many generations, based solely on selecting traits based on what was most desirable in the current generation. With GMOs, we can greatly change very fundamental things about an organism in a single generation, and the question that hasn't been answered in a manner that is acceptable to macro-ecologists is if it's even possible to do that in a way that doesn't have potentially expensive ripples. I suspect that the answer to that question is that no, we can't have GMOs that don't have a severe impact on the ecosystem around them, and I don't think we're ready to be exercising those changes.