What do you think is going to happen if farmers start selling their land for building residences and offices? where do you think your food is going to come from? Corporate farms? do you seriously think corporate farms are going to be carrying more for the environment than farming families?
I think they might actually now that you mentioned it. In the same way h&m has a better policy than most locally owned clothing stores. Families typically face immense pressure to only think about the short term. But it wasn't what I was thinking of.
But like I said the food produced by land that is urbanized would have to be imported. But that is not a bad thing. It will be very good for developing nations.
Not producing food locally and being dependent on imports for even basic food supplies is actually even more dangerous than being dependent on other countries for stuff such as electricity. Plus consider the huge amount of energy needed to transport food crops across the globe.
Another question worth thinking about - what landscape pollutes the air/water/land more? is it farm land or the cities?