This article sums it up better than I can. And provides many reasons why GM Crops and foods must be labeled for consumers.
GE Crops and Unsustainable Agricultural Practices are Destroying our Planet’s Soil and Food Supply
Genetically engineered crops and food products pose a threat to your health, resistance to disease, soil, and the global food supply. The biotech industry is riddled with corruption as companies clamor to sink their claws into the marketplace first, to get their seeds into farmers' fields ahead of the rest.
Read more here, please: GM Crops pose worldwide danger