Many people are suspicious of GM food as there is no long term safety testing. Genetic engineering uses material from organisms that have never been part of the human food supply to change the fundamental nature of the food we eat. Without long-term testing no one knows if these foods are safe.
There are also concerns that GM food could contain harmful and carcinogenic toxins or leads to allergic reactions. Genetically modified food may trick consumers with false freshness. Something may look fresh, but in reality it may be months old.
Genetic engineers use antibiotic-resistance genes to mark genetically engineered cells. This means that genetically engineered crops contain genes which confer resistance to antibiotics. These genes may be picked up by bacteria which may infect us. When this happens, we would be powerless against these bacteria as they are immune to antibiotics.