Pesticides of various sorts have been used for thousands of years to fight against the infestation of bugs in crops. However, overuse and use of unsafe pesticides have resulted in damage to cropland, animal and plant life, and harm to humans and human children.
The biggest argument against pesticide use is the concept of residual chemical buildup; since a certain amount of pesticides are retained in edible crops, that pesticide is in turn consumed by people. Some studies suggest that buildup of these compounds can cause birth defects, neurological defects, and higher incidences of cancer. Not all of these studies have been replicated or proved, but many of them are peer-reviewed and accepted as fact by the scientific community. If pesticides cause this harm, then it is important to limit their use so as to avoid needless deaths.
Another concern is generational immunity of infesting pests. If pesticides are used improperly, they will not kill all the bugs in the infestation, and the surviving bugs will reproduce new bugs that may have resistance to the pesticide. While stronger pesticides may be used to kill the resistant infestation, this can cause a higher incidence of chemical buildup, with possible results as indicated above.
It is important to note that long-term use of powerful, artificial pesticides is still under study; shock stories in the media have created a skewed public view of pesticides and their effects. While studies are continuing, many people prefer to choose organic foods which may have fewer or no pesticides used during their cultivation.