"Telephone operators being fired didn't stop us from switching to digital phones. Why coddle farmers more?"

or a bit longer:

"People aren't entitled to doing a job that harms everyone else. If a plumber only knows how to work with lead pipes, we don't have to poison people just to prevent the guy from having to learn something new.

It's our job as a society to take care of people who become unemployed because they only know how to do harmful jobs. To help them retrain if they can, and ensure they have a comfortable lifestyle. Farmers that would face bankruptcy deserve a bailout, and like everyone, all farmers deserve a universal basic income/universal basic services".

It is not wrong that farmers would be screwed financially if a government goes as hard as it needs to on sustainability without shielding farmers.

In terms of assets, pretty much all the industrial equipment and many of the buildings of a 20th century industrial farm would be useless in a sustainable farming setup. Obviously all the animal torture factories would have to go, but what use is a combine harvester in a food forest? Also, between the 4-fold reduction in crop production because you no longer need to feed farm animals, the reduction of food waste, and the higher yield per acre from sustainable farming, the price of agricultural land itself would also plummet.

This means that pretty much every industrial farm that has leveraged its assets for a loan would be financially screwed, and so would every bank and investor that gave out those loans without accounting for this possibility. A capitalist stock market would be shocked by your government choosing a healthy country over private profits, and this could cause a financial crisis and economic depression without either a slow ease-in by the government or seizing investor assets in a coup or revolution.

Furthermore, in terms of labor, the current skillset of industrial farmers has remarkably little in common with sustainable agriculture. All they know is torture animal, drive combine harvester, exploit they workers, be conservative, poison land, and lie. So while we may even need more farmers for sustainable agriculture than for industrial agriculture, many people who are farmers right now would probably need to start at ground level, knowing less relevant information than a gardener.