"Organic" methods produce considerably less food per unit of land (and other inputs) than conventional farming [0] (that being one of the reasons for the price difference). How does that make it "more sustainable" ?
"Right now, roughly 800 million people suffer from hunger and malnutrition, and about 16 million of those will die from it17. If we were to switch to entirely organic farming, the number of people suffering would jump by 1.3 billion, assuming we use the same amount of land that we're using now."[0]
... and yet the world produces on average more than 5000 calories per person. Is "increased productivity" really what we require?
There is also the issue that the idea of greater productivity is highly geographical and seems to be valid in the context of European and North American monocropping agricultural systems. Other farming systems may produce a lot more overall nutrients - it is not at all clear that systems fueled by synthetic fertilisers are more productive as far as overall ecnomic/livelihood benefit or nutrients are concerned in East Asian and African agriculture. Results got from research done in Europe and North America (greater productivity in monocropping non-organic systems) are often suggested as valid in the context of "ensuring sufficient food production Africa / East Asia" which at least from what I know of Bengal seem to be a truth which requires substantial modification (see for example a relatively conservative discussion in [1]).
Further, Rodal Institute's longitudinal study[1] seem to suggest that organic practices can indeed match conventional.
Finally - hunger and starvation is generally not an issue of too little food production as Amartya Sen's nobel prize winning research on Bengal famines highlighted.
