Pesticides allow us to produce more food, which cuts the cost of the food we buy. So pesticides are especially important in places of the world where people can barely afford to eat. But many pesticides are also poisonous to humans, so we have to make sure they don't contaminate our food, water, or air. 

Pesticides are used to get rid of pests from many places, not just food. For example, wood in buildings is often treated with arsenic or other chemicals to prevent termites. This is relatively safe unless you burn the wood or eat it. (Arsenic is an element, so it's not destroyed by fire.) And preserving the wood with pesticides also saves our natural resources because we don't have to cut down new forests to replace the wood. 

Another important example is mosquitoes, which carry malaria, West Nile virus, and other diseases. Without pesticides to kill or repel mosquitoes, many people would die from these diseases.

There are safer types of pesticides now, but unfortunately, many dangerous types are also still made, sold, and used. If you pour pesticide into a lake or pond to kill mosquitoes, you kill all the mosquitoes, but you also kill all the fish, frogs, birds, and bats which eat mosquitoes and their larvae. So then, the next year the mosquitoes come back much worse than before.

Water that contains pesticides runs off of agricultural areas and contaminates groundwater and the ocean affecting the health of humans and the environment. There can also be health concerns to humans directly from the consumption of pesticide-containing produce and especially for the people spraying the crops with pesticides.

Many pesticides are distributed through the air. This means less than 10% of the average application will even reach the crop and less that 1% will even hit the intended pest that needs to be removed. 

Though the disadvantages of pesticides are endless, usage of pesticides leads to more profit which is why farmers tend to neglect the cons and this is why it is our responsibility to educate our farmers about healthy and safe farming around the world.