It results in the creation of monocultures. No genetic variations as normally found in the wild. So many other issues.
Monsanto created a "roundup-ready" canola. This means that round up, which I believe is a carcinogen (could be wrong about that bit), can be sprayed over entire crops. The idea is that instead of cultivating rows of plants, they want to just spray fields to eliminate weeds. The canola cross-germinates the weeds, and then you have a super-weed. Monsanto then needs to make more-deadly chemicals to kill the weeds. Endless cycle...
Then there is the pollination mentioned above. See
http://www.percyschmeiser.com/ for what happens. The legal environment that is being created around this entire industry is unbelievable.
Next you have to look into the corn crops (and forests) that are modified to generate a natural insecticide (also refered to above) as being responsible for killing monarchs. The problem here is that the natural plant expresses this substance in small quantities. You can even buy it at nurseries to kill tomato worms. But in a corn field, or a forest, with every gene of the plant expressing this crap 24x7 - well, what's it doing to the environment. What do we not know after allowing this crap into the environment for less than 10 years now. What will we know in 10 more years? 20? See the problem? They want to play God. Not a good idea to mess with nature.
Then you look at GMO (farmed) salmon. These are modified genetically to encourage rapid growth. Much of the "farmed Atlantic salmon" is raised offshore in Chile in pens. The pens are huge nets painted with a anti-fouling substance that prevents the growth of significant vegetation, but not 100 percent. That paint is toxic. The small fish that feed on the growth from the nets have some undetermined level of toxicity. The salmon that feed on those small fish are consuming that toxicity. Yummm...
With all the fish penned in this unnatural enclosure, the waste settles to the bottom in unnatural quantities. That is creating immense dead zones at the bottom of the ocean.
Occasionally the pens break. These unnaturally large fish have been determined to be sexually agressive, and more-attractive spawning partners, but less effective breeders. That is believed to have impacts on the offspring when breeding with natural fish.
More reading here: www.sacmobilization.org
It took my lady and I a day of attending the pre-mobilization teach-in to make us devout consumers of organic foods, and fierce opponents of GMO. We spent 4 days running around Sacramento disturbing the peace and getting chased by robo-cops.
What a fun world we live in. Makes ya hungry huh?