How are pesticides bad?

Yes pesticides are some what bad because of what they do, they kill insects. They also go threw the ground and eventually end in water making pollution... Some of the insects that the pesticides kill are actually not going to hurt the plants that the pesticides are on in the first place. that means pesticides kill and pollute, does that sound very good. Pesticides are made from chemicals, bad ones at that and poison's in poison's out.