Harmful crop breeds would have been selected against over the course of many generations, right? Now we're doing it on a larger scale, so the risks and rewards

Harmful crop breeds would have been selected against over the course of many generations, right? Now we're doing it on a larger scale, so the risks and rewards are greater. What is our knowledge of the risks and rewards? Are the rewards aligned with general human wellbeing, or just a profit motive? I don't know.