I am more worried about the follow-on effects than GMOs per se, for instance when crops are modified to be immune to herbicide farmers will no longer have any incentive to moderate their usage.
The other side of this is farmers modifying plants so they don't have to use as much fertilizer, pesticides, or water. It seems those positive aspects dominate the externalities issue.
I was raised to believe that genetically-modified foods are unhealthy to eat and bad for the environment, and given a variety of reasons for this, some of which I now recognize as blatantly false (e.g., human genetic code is isomorphic to fundamental physical law), and a few of which still seem sort of plausible.
Because of this history, I need to anchor my credence heavily downward from my sense of plausibility.
The major reasons I see to believe that GMOs are safe are:
The major reason I see to believe that GMOs are dangerous is:
So: green goo, yes or no?