If the US only allowed one grocery store to exist, that would have economies of scale as well.

Shouldn't we then give everyone "food insurance" which you pay for with taxes, and then are able to use that food insurance to get food from the store for free? (well, not really free, paid for by your taxes). You'd pay a predetermined amount of money no matter what you got from the store, but your options would be limited by the government food insurance committee.

If you don't support this single payer food insurance solution to all of your caloric needs, then my question for you is why do you hate poor people?