no duty to anyone ? individualism gone a little too far, methinks. you have plenty of duties, most of which you do automatically out of respect for society, societal expectations, morals and legality.
choosing to buy from someone who understands their land, what's in the long term interests of it and their animals sounds like a wise choice to me and means you can make a difference without spending any more in most cases.
eggs - good example. I pay £3.50 for 30. local place, set up a vending machine arrangement so unattended. down the road. cheaper, faaaaaaaaar better than Tesco. required a little investigation and time to find it. most small businesses just struggle to reach people so they're aware of it. if you compare that to the labour, capital and all the rest of Tesco - what do you think you're paying for? it's not really the eggs.
the thing most people choose is convenience all under one roof - in / out, click/collect, under an hour.
shit, I actually agree with Ash