> they'd grow diversified crops to sell locally
This is out of touch, many of these farmers are 100+ miles from a large population center. They can’t move enough produce at a local store to stay in business.
And conversely you can't grow enough food local to a large population center to feed everyone.
Maybe, but it's not an argument against diversification. When it comes to agriculture, the incentives should be aligned such that a single point of failure like this is highly unlikely.
That's not to say it's an easy problem to solve.