I don’t think all genetically modified foods are necessarily a bad thing if done with the right motivation and properly labelled so that people with allergies can avoid things they are allergic to.
They aren’t largely done with the right motives however, especially when Monsanto is involved. Then you can be sure the only motivation is profit and they don’t care how many people they kill in the process. Instead on concentrating on making plants a better food source, they concentrate on making them resistant to carcinogenic weed killer, to making the seeds non-viable so farmers have to buy seed from them every season, etc.
Even with the right motives though there needs to be adequate safety measures. For example, rice is what is known as a C3 plant. C3 plants are inefficient in their use of water and are in areas with a lot of sunlight, less efficient at photosynthesis than C4 plants.
Rice is a staple food source for half of the worlds population but it requires a large amount of water to grow and thus can not be grown in more arid environments. There is presently work to develop a C4 version of rice. If this work is successful, it would allow rice to be grown in areas where water is less plentiful and in some regions it might allow it to grow faster because of more efficient photosynthesis.
A danger I see with this is whether the C4 version of rice that might exist is that it might have less nutrients than the natural version. The why of this is related to the more efficient use of water. Plants bring water into themselves by osmosis, and along with that water they bring in many minerals that they don’t need for their own growth, but we do.
If you increase the growth rate or reduce the amount of water they need to grow, along with less water intake, they will likely also take in less minerals, that we need. So while the resulting crop might meet our caloric energy needs, it won’t meet our nutritional needs.
If a gene is taken from another food crop plant, then it probably isn’t going to introduce any new toxin. If genetically modified foods were required to be labelled with where the new genes were taken from people with allergies to the source organisms could avoid them. But there is still the issue of if you make a plant grow faster with less water, what happens to the nutritional content, especially the mineral content. That needs to be assessed and publicly disclosed, and thus far those behind the GMO development seem to want nothing to do with public disclosure.
If they have their way, we could all starve to death in the midst of a glut of food.