Playing Devil's advocate here.
DDT-Saved inordinate numbers of people in the 1940's-50's by eradicating typhus spread by insects along with Malaria and Dengue fever. Once the side effects were realized, DDT was banned for use as an insecticide. However, there are many alive today especially in the Far East and Europe whose parents/grandparents would have succumbed to one of these diseases.
GMO crops-The weeds are resistant due to the farmers not applying enough Roundup (glyphosate) to their fields and killing all weeds. If you lower the usage rate by 1/4 or 1/2 (original Roundup was put on at 32 oz. per acre and many farmers tried to get by cheaper by lowering the rate) you are not going to kill all the weeds in the field. Weeds that are not killed can go on to reproduce seeds that have some resistance to the herbicide. After several generations of this, the weeds have a tolerance for glyphosate and it does not kill them or even harm them.
-One other thing about GMO crops-food stays a lot cheaper. Hogs, chickens and cattle are feed corn and soybean [mixtures] that are the cheaper GMO grain, besides the amount of corn used in meal, sweeteners etc...If we had to go back to non-GMO seeds and the herbicides that we used 20 years ago, you would see a substantial rise in food costs. However, I do not agree with Monsanto successfully suing organic farmers whose crops were cross pollinated with GMO crops.