The assumption that we can better determine toxicity with our current understanding of human biology than thousands of years of natural selection seems questionable, but peanuts are certainly a good lower bound on selection's ability.
I also don't have much confidence that the parties responsible for safety testing are particularly reliable, but that's a loose belief.
Natural selection wasn't attempting to make it harmless to humans. Especially in plants that didn't evolve nearby humans.
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?