I did a paper on this a few years ago, so my mind is kinda rusty, but look at europeans, and their websites, as the eu has banned GM crops. This is what i remember:
My suggestions for your debate is to focus on a few crops and to know a lot about the modifications that have been done with them.
Corn was modified to create a strain that was resistant to some worm, and they modified the dna. . . sounds like a good idea right?
The idea was that the corn's toxins would create a feeling in the worms gut that it was full and the worm would starve to death.
What if that "benifit" was passed on to humans? Would we all stop eating?
Also, look into how corn reproduces. (hint, by air, and the pollen is spread long distances, aka: if we had a problematic strain of corn, we might never get rid of it.)
Also, the original strain of GM corn was called the terminator, because it only was good for one year, aka the seeds were not viable. This caused the farmers to have to buy seeds every year. hummmm, wonder if this could be passed on to humans. . . .we are eating the seeds, and would that make our kids not feritle. . .
enough about corn
Next, modifying rice or food stock to increase the production sounds good, but what happens to the soil? You might be able to double your production for a few years, but then the soil is depleated and you are back to less and less food. . . reciepe for disaster.
Dont get me wrong, i am a fan of modifying crops, but there is a way to do that, it is called hybridization. Lets not mess with the dna of crops, we just dont know what we are doing.
Hope this helps.