Problem with chemicals is that over time they or the stuff they break down to will accumulate in the nature and who knows what issues it will cause. Once the chemicals enter the nature they are going to stay there.
In example pesticides. They kill everything. When I was a kid I remember walking in a meadow it was full of bugs, lot of grasshoppers and lot of animals that feed on insects. There were birds, lizards, snakes, all kinds of birds etc. Agriculture killed their source of food so they disappeared. After that application pesticides increased. When I go to visit places where I grew up there are no lizards, no meadow larks, no crickets, few grasshoppers, very few flowers in meadows. You want to see all what was common everywhere in the past you have to go to undeveloped places not used for intensive agriculture. And those are harder to find as time goes by.