My issues with GMO's are along the lines of TK.
I have no compunctions with genetic engineering. Mankind has been genetically engineering things since we first settled and formed civilizations. We domesticated animals. We domesticated plants. We bred both to benefit us. Just because we have the technology to do so through laboratories now doesn't make it bad.
However, I do think we have a tendency to release genetically engineered products to the general populace far faster than we should, without adequate trials to determine the full adverse effects that could occur.
But even worse, we allow evil behemoths like Monsanto to dictate the distribution of these things.
I'm a free-marketer at heart. But much of what we do is closer to corporate socialism than actual capitalism. It's Murphy's Golden rule, and Monsanto has all the gold to make the rules. They are one of the few truly evil corporations out there. They don't believe in free markets; they only believe in their market. In the end, society, while maybe not losing, will not benefit nearly as much as it could.