You'd be surrendering colossal economies of scale were you to do that, causing much higher food prices. Most people in big cities don't care to grow food, and most people who grow food don't care to live in big cities. The parent with whom you're agreeing also mentioned a lower local diversity of things grown, which means that to get a decent variety of stuff, that actually increases reliance. I think if anything, we're going to see a desire to become less reliant on others (especially internationally) which will drive people to grow a larger variety of crops locally.