Sure, there might be potential benefits to these kinds of manipulations, but we need to do a far better job of understanding their impact before turning them loose on the only planet we have.
Here is a case in point. Scientists at Cary Institute of Ecosystem Studies, publishing in the National Academies of the Sciences found maize detritus in 86% of stream sites surveyed. Of these 23% had proteins derived from Bacillus thuringiensis (Bt corn) in their water column. All of these sites had Bt corn planted within 500 meters. The Bt protein, which is closely related to B. anthracis, the agent behind anthrax, is highly toxic to a number of insect species, beyond the specific caterpillars against which it was targeted. Among these, are the chironomidae, or non-biting midges, commonly known as lake flies.
These insects are important food for fish such as trout and sturgeon as well as insectivorous birds such as swallows and martins. In fact, many of the fishing flies that anglers use are fashioned in imitation of these little guys. Earlier studies have suggested that Bt corn might also harm the caddis fly, another important fish food.
We develop a new technology that supposedly produces more corn, but we end up with less fish.