Yes but we can all grow tomatoes or bell peppers if we have a balcony, not enough but why not.
Cities could locally grow some of their vegetables if neighbors have a community gardens in some roofs, collect rain water to save money, etc. Based on your name I think you live in SF, right? Go to talk to any hippies/hipster, they're very educated on the subject.
farm raised fish also doesn't require much effort Istanbul's underground cistern Obviously not ALL of our fish should come from farms just like it shouldn't come from a can of tuna potentially loaded with mercury.
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I'm not saying cities could grow all their vegetables and fish, but doing something is always better than doing nothing specially when we know we can't do everything.