It is just a natural part of farming, something farmers have been doing for thousands of years. Selective breeding is a form of modifying a plant, or beast. Thus, our cattle, and other animals, and corn, and other plants are nothing like the wild ones.
Modifying the genes directly is just another step, now made possible by modern science. So, producing a plant that resists disease just makes sense. Of course, people get freaked out by modifying the genes, even while eating bread from wheat developed by scientists through breeding, and beef that barely resembles the wild cows it was developed from. It is the "mad scientist" thing that people are afraid of, and, the apparent lack of knowledge as to what the new GMO foods will do to the environment.