Pollen from GMO plants can (and do) cross pollinate with organically grown plants of the same species (corn with corn, soybeans with soybeans, etc.), which results in contamination of the organically grown plants.
It really depends what type of genetically modified crop it is
There are millions of effects brought on by genetically modified microbes and pollution control. This can make a portion of the population Êphobic of anything dealing with the government for example.
We have genetically modified foods for centuries by selective cross breeding plants. With out this and other modern methods of farming perhaps a billion people now existing on a substance diet would starve to death.
a child who is starving
People who live in a poor village.
Genetic Predisposition is a genetic effect which influences the phenotype of an organism but which can be modified by the environmental conditions. Genetic testing is able to identify individuals who are genetically predisposed to certain health problems.
Some argue that genetically modified food has no effects on human or animal genes. They also argue that GMO foods are the same as any other foods and have no negative health effects at all. Others argue that they might cause changes to our genes, and that they do cause changes to the flora in our intestines, possible sterilization, and other health issues. The FDA has declared then to be "substantially equivalent" to non GMO foods. In reality, we just do not know what effects genetically modified food have on our health or our genes.
People are concerned about this because genetically modified food is not natural food. It was genetically modified by a human or a machine. In either case, man made machine, and man isn't perfect. So, because of that, people are so concerned.
This is already in effect nowadays. The FDA allows companies to sell genetically modified food, which theoretically is unfit for human consumption due to potential health reasons.
There are no scientifically proven effects of any kind. However, as with any new technology, there is much rumor and conjecture, from simple allergies to the notion that it could somehow change the human genome.
That depends on what you mean by "What can we do…" If you mean how can we stop GMO foods or how can we avoid eating them, the answer is simple. Stop buying foods that you think might contain GMOs. When food manufacturers' profits decline, it does have an effect. An example is Cheerios. Apparently, sales dropped to the point that General Mills was losing money, so they modified the ingredients to eliminate GMOs in Cheerios.