Probably the biggest threat of GMOs is that if you can make them more resilient to a herbicide, fungicide or what have you, that you can also make them more vulnerable to some substance that could then be later used to trigger famines.
Except you don't advertise that.
https://news.ycombinator.com/item?id=12015572
And after reviewing that thread again, it appears such technology has already been commercially developed (https://en.wikipedia.org/wiki/Genetic_use_restriction_techno...). Although in this instance it doesn't make the plant susceptible so much as it creates a food system dependency on the company that sells the GMO in order to grow the food in the first place.