There are three problems:
- the most obvious, concentration of market power. Just look at the stranglehold large corporations have over politics - Walmart is for example famous for getting away with underpaying their employees so much they have to apply for food stamps, and local politicians or unions are unable to do anything against it because Walmart can at any time decide to just close shop and leave an area completely without access to groceries (made possible in the first place because Walmart systematically undercut local stores on pricing). And people (i.e. voters) would not blame Walmart, but local politicians and unions. No one wants to add yet another mega-corporation to depend on for survival.
- second, concentration of genomics. When everyone and their dog sans a couple eco activists and seedbanks raises the same variety of crop or the same breed of farm animal, pandemics have an incredibly easy game. The best warning sign what can happen in such monocultural environments are forests (where bark beetles and other pests run rampant and completely destroy them) or bananas (Gros Michel famously got wiped out by a fungus and Cavendish is at the cliff from another fungus).
- third, the impact of pesticides as a whole. No matter what kind of pesticide, they all have serious side effects - most notably, they cause bees to die and as a result, all plants depending on bees for pollination can't reproduce any more. And ffs it's not just bees. All kinds of insects suffer, just compare your windshield after driving a car in the 90s and today through a rural area. And all these insects were part of the food chain for larger animals... leading to an ever growing loss of biodiversity further up the chain.
> But we must also abandon pastoral aspirations of converting farming back into a hugely labor intensive activity as it was, say, 150 years ago. Except for the few that want to do it as a hobby, our backs will thank us.
We don't need to go back that far in time. Like half the food produced is wasted instead of reaching a human's mouth - spoiled, rejected for missing quality benchmarks, never sold because stores require an overabundance of choice for the consumer, wasted because restaurants prefer to deliver too large portions because they are afraid of bad Google/Yelp/... reviews... the list of causes for food waste is immense. Cut down on food waste, produce less food in total, and maybe avoid the need for intensive agriculture in the first place.