This is based on existing farming practices and the second and third order effects of using crop land. It’s entirely possible to grow plants without harming animals, but it’s impossible to eat meat without harm (barring research into lab-grown meat)

One can envision a future where more crops can grown on a smaller footprint with future agricultural developments (e.g hydroponics, multi level farms, etc)

It also ignores the fact that the production of red meat is incredibly bad for the environment, and one of the large contributors to greenhouse gases.

This argument feels similar to criticisms of electric cars because generating energy currently hurts the environment, but this ignores the future potential of widespread renewable energy, with which petroleum vehicles are incompatible.