What Frank said.
I have a son and daughter in law both working toward advanced degrees in environmental science, we've talked about this a lot. The real complaint against GMO's is not that they are dangerous to eat (as Viv pointed out, they aren't). What we don't know is how they will effect the environment, and the plants around them.
If we could insure careful handling, and move slowly in allowing them, I'm OK with it. But we need to be careful and study the problems as we go.