1) when talking about sustainability, should you consider "economic sustainability"?  some say you should. In other words, if the farmer is not making enough profit to stay in business, then that system is not sustainable.

2) what about the use of petroleum fuels?  (you did mention them).  So, if you really want to talk about (environment) sustainability, you would need to eliminate the use of petroleum from the system.  That would mean going back to using hand labor to grow food?  That would mean that going back to a system where a large majority of the people would be involved in the production of food(?).  If one studies history at all, one would realize that it is the mechanization of agriculture which allowed more and more people to move away from the process of growing their own food, and allowed civilizations to become more advanced and more complex.   That's the whole point of what we are doing - allowing fewer people to grow the food, so more people can devote their time to other pursuits.

And the debate goes on..... and on...... and.....

:)