The main reason that I'm wary of GMOs: not enough time for testing. Any medication, any technology, anything that may affect the body, it sometimes takes a generation or more to find out the side effects. What seems perfectly sensible, logical, rational in the now may spawn unexpected consequences 40-50 years from now. I try not to be an early adopter of much anything for these reasons. Also, I'm old enough that my inchoate, knee-jerk response is that GMOs come from the devil, and microwaves are the spawn of Satan, but I know that's because of my age.
Inversely, some years ago, when I had a cat, I posted to my online blog how I was making my own cat food, listing out the ingredients, the research I'd done, how much better my cat seemed to be doing (damn, that cat's coat got glossy). And it boggled my mind, the responses I got from people saying what I was doing was wrong, that the only thing you're supposed to feed cats is pre-manufactured, commercial canned and dry food. Sometimes technology comes full circle and spawns resistance and stupidity.