All foods sold in food chains must be labeled according to the FDA. However, the issue here is that GM foods aren't labeled as such and responsible consumers want them to be so that we know what we are eating and risks we take when we still choose to eat them. You would think that foods bought from farmer's markets are better and, to some extent they are except the seeds used are seeds produced by Monsanto and company. Real organic seeds are becoming extinct now because you literally have to cultivate them and harvest them from the original plant source. Buying seeds from a store is pretty much a guarantee that Monsanto produced them even if they claim to be organic seeds.
There have been studies done that link GM foods to certain health conditions so I also believe that GM foods should also be required to be labeled as a health risk by the Surgeon General the same way cigarettes have to be labeled. Unfortunately, as in everything else, GM foods are cheap so once again this is an issue of economic injustice for the poorest citizens. Health costs will increase due to an increase in illnesses, mortality rates will increase if you can't afford good medical care, and worse, if you don't actually die from affects on your health, your quality of life is compromised tremendously. But who is associating all of this to GM foods? Are doctors being trained to pinpoint certain illnesses to GM foods? People just want to assume that poor people just have bad eating habits thus they suffer from illnesses caused by eating unhealthy foods.
Here is a link to one website that could help us to learn about this more:
http://responsibletechnology.org/gmo-education/health-risks/