Genetically engineered crops have both pros and cons.
For example, scientists can insert a gene into plants for drought tolerance. If these plants are planted in an area that has a drought, they will be more likely to survive and produce healthy crops. Another pro of genetically engineered crops is pest resistance. Using crops that are genetically modified to resist pests means that less chemical pesticides will be used on them. These kinds of crops can also be modified so that they are resistant to cold weather and disease.
Some cons regarding genetically modified crops are related to the environment. Some people fear that these crops may be harmful to other organisms. In addition, it is feared that pests, such as mosquitoes, will become resistant to these kinds of crops. There are also concerns related to human health such as allergies and other unknown effects.
One of the cons has been the incredible ability of a small group of companies to take over the rights to so much of the world's seeds. If you look at the news, there are currently those who would like to bring anti-trust suits against companies like Monsanto, but they are so powerful and so large, that it will be difficult to do any great harm. If you watch Food Inc. you can see some of the problems with genetically modified crops growing next to those that haven't been. If the new seeds or plants spread into the field that had regular seed, the company that owns the seeds can actually claim the crop on the land which was originally planted with normal seeds as their own.
These crops also tend to encourage the growth of all kinds of resistant pests requiring further modification and further use of different pesticides, etc., driving up prices for farmers and putting them further in debt to their suppliers, a dangerous situation for them and our food supply.