I grew up on a farm and have continued to raise plants for most of my life. Anyone who does this usually learns about insects that prey upon plants. The smart ones also learn about the balance of nature.
I have seen cut worms, aphids, mites and hoppers destroy crops and the plants that produce them. I have seen how practising mono culture, that is growing huge, unbroken areas of a single crop, has facilitated terrible infestations by providing and almost endless feast of a favoured plant for a pest.
I have seen pest control that did more harm than good by killing not only the targeted pest, but directly or indirectly also many benificial organisms. Collateral damage, so to speak.