From a conversation I had once with a pair of starry-eyed young petitioners, I get the impression that the main objection some people have is that GMOs are made by "giant corporations." I decided not to bother pointing out that their iPad they were asking me to sign, as well as their jeans and sneakers, were also made by giant corporations.

IMHO it's because of a clear pattern of attempts to do artificial things to food turning out badly. Trans-fats are bad for you. Artificial preservatives are bad for you. Nitrites are bad for you. There's a lot more.

People don't understand the technology but they do see the general pattern here.