The "Millions Against Monsanto" campaign is fighting for transparency in labeling, an issue which causes tremors amongst the food industry. While almost all of us have eaten genetically modified food of some sort, a 2006 survey by Pew indicates that less than 30% of consumers think they have - probably because there is no requirement that genetically-modified food be labelled. On the other hand, food producers are worried consumers are much less likely to buy foods if they have scary labels with scientific terms on them, and Monsanto claims that genetically modified foods have no proven health risks. [Full Disclosure - I am a member of the OCA, but do not plan to participate in this protest.]
The problem gets even more complicated. In order to get USDA organic certification, a product cannot contain GMOs. Whole Foods also has started a program, through the Non-GMO project, to make sure that their store-brand products are GMO free. But, Whole Foods (despite its environmental credentials) still carries many conventional products, which may contain GMOs. Should they be forced to label them?