Genetic modification doesn’t bother me, except for 2 things:
1. When it makes a plant resistant to poisons that kill everything else, because that encourages the use of that poison. For example Roundup, containing Glyphosphate herbicide, has been shown to be a persistent toxin in the soil for years and negatively affects crop productivity in clay containing soil, as well as fish, animal, insect, and nitrogen-fixing bacteria populations , .
2. Legal compulsion bothers me too. For example: Multi-billion dollar corporations using the benign qualities of genetic engineering to excuse corporate hegemony of world food resources through patents.
Monsanto manipulates market demand through politics and advertising, to make a major food source (and thus everyone using it) dependent on a single minuscule genome. The modified plants (AKA Roundup Ready seeds) only unique survival trait being a resistance to a particular synthetic herbicide, while being completely dependent on major capital, legal, and media support.
Imagine a zombie apocalypse where all the survivors live in scattered dwellings, each with one door (each door is a unique genome). Occasionally a door gets breached and the occupant gets eaten up but it only affects single individuals and not the total population. Then someone (probably a corporate lawyer) advises everyone to move together and live in a mall, also with one door. What could possibly go wrong?
Check this Video about Monsanto (theguardian.com and theundercurrent.com)