Many farmers will receive a one-time payment on land sales and some will use this windfall to subsidise their transition from growing livestock to more environmentally-friendly food.
This assumes that the land is equally usable for both activities. Many times, it isn't: a lot of land that's good enough for grazing cows doesn't have enough water available for growing plants that people want to (or can) eat. People can't eat grass.
This probably isn't an issue in Denmark, but in many other places it is.
Just because plastic bags are ubiquitous doesn't mean it's the only nor best way to carry items around, nor that we'd lose the ability to transport goods if they were phased out, nor that they don't come at a cost despite perceiving them as free.
Crop soil needs fertilizer somehow
What is your alternative to manure?
Bonus points if it uses less energy to produce than animals, produces less CO2 than animals, takes up less space than animals, or also produces food at the same time
Cows are so inefficient that we don't need to use marginal land at all to grow food. The majority of arable land is already used for cows yet they produce a disproportionately small amount of food. Weening off cows is a good thing.