In decades past, organic farming or sustainable agriculture were discredited among farmers as being a movement to return to 18th century farming practices. Chemical and fertilizer companies used these images to impress farmers that if you wanted to use any alternative to "modern" farming practices you would probably be spending a lot of time looking at the wrong end of a horse. But, 18th or 19th or even early 20th century farming practices were just as destructive as today's practices.
So, how are we supposed to feed ourselves? We do it through agriculture. Anyone who thinks I am suggesting we quit farming and go back to hunting and gathering is jumping to conclusions. The problem with agriculture has always been the way it has been done. From slash and burn to no-till industrial chemical agriculture, through centuries of human attempts at raising a crop, the impact on the surrounding area was of little consideration.
In the 1970's American farmers were encouraged to take out all their fence rows and plant every available inch to maximize their profits. This attitude was fostered to not really benefit farmers but rather to benefit companies that farmers sell their products to. So what, if you gained ten acres more on a thousand acre farm. The benefit was not that great because the price of corn was low.
Along with taking out the fence rows farmers plowed their pastures, took out timber, and otherwise degraded their properties in search of profits. Or, maybe it was not just profits but a desire to participate in the otherwise booming consumer economy at a level similar to laborers or other people who actually worked for a living. The effect of their activities was increased erosion, destruction of wildlife habitat, loss of biodiversity, and increased run off of chemicals.
Agriculture by nature is a disruptive activity. But, how much agriculture do we need? How much of the millions of bushels of grain actually go to feeding people? Is feeding the grain to livestock and then eating the livestock really worth the amount of resources and environmental destruction that is the result of this practice? A trip to a grocery store reveals aisle after aisle of things people can eat. But so much of it is so processed the actual food value is depleted and some of it is such a toxic mix of chemicals and additives it is not worth the energy used to produce it.
The best days of Human Agricultural activity are still in the future. Until the full impact of agricultural practices on the environment are reflected in the final cost of the product on the shelf, agriculture will continue to be a wasteful destructive force.