Nobody really knows what the effect of genetically modified organisms can be on the ecology as a whole. The argument is on going ahead with the technology because of the huge efficiency benefits or ceasing (or at least slowing down) until we know more about the short-term and long-term effects.
I was talking about this with a friend yesterday and realized that I did not mention labeling, though it was in the links I added.
In the US, the big argument now is about labeling. GM labels are not required by federal law.
The arguments against labeling are that GM crops have been used for many years now, no harmful effects to humans directly from eating GM food have been conclusively found, and labeling would essentially be a scare tactic because it would freak people out when they realize that pretty much any grain based foods and many vegetables are GM. Similar to labels with the word 'irradiated' which implies nuclear radiation to the layman when in reality it is a much more benign (though not necessarily worry-free) process.
The arguments for labeling are that more information is always a good thing, and that while GM foods may not have been shown to have a direct effect on human health, GMO in general can have an effect on the ecology at large and people should be able to know what products they are buying and thus what type of industrial processes they are supporting. Being in favor of labeling does not necessarily mean someone opposes GMO technology in general.
The consensus on the effects of GMO on ecology is leaning towards them being disruptive, but that's not necessarily a negative thing in every case. As much as we know about DNA at this point, it is still a black box in many respects, and the cascading effects of seemingly harmless genetic modifications is an even blacker box.
So, like most important arguments it comes down to where you prefer to place the risks. Risk potential ecological side effects but grow food more efficiently and feed more people, or risk higher costs and food shortages but be cautious about introducing 'unnatural' organisms into the world. And, like most important arguments, the logical answer is probably somewhere in the middle and most people (groups of people, not individual persons) will tend to gravitate towards one of the more illogical extremes.
Hope that helps put it in perspective. I've tried not to let personal biases into it, but honestly I don't even know what side I agree with more here.
Are there risks with GMOs? Maybe and we need to proceed cautiously but as an agronomist for over 30 years, here are benefits: 1. Less use of pesticides, especially those more potentially hazardous. 2. Increased crop production. We aren't finding more arable land and in fact we have less for a variety of factors. We need to increase efficiency and decrease losses from pests (insects, diseases, and weeds)while figuring out how to feed another 2 billion people in the net 25 to 30 years. 3. We can and have produced crops with special traits that can do things like prevent blindness in the developing world and producing food with vaccines in them that don't require refrigeration. 4. The area of adaptation for certain crops can be expanded. There are more benefits but that gives you an idea. I am all for labeling and wish we would just do it.