Modern society relies on mass scale agriculture which cannot be replaced by community gardens. If everyone had to meet their nutritional needs with a community garden that is within walking distance of where they live, we basically couldn't have cities.

Growing your own food is work; where is the retirement plan? What if you're not able? Even if you are, many people want to do things other than farming when they retire.

It feels like the ultimate defeat: what have I achieved in this lifetime of work, when I'm reduced to land-to-mouth existence, like an ancestor tens of thousands of years before me? Where is the progress?

Theft is a problem in community gardens. If you just grow enough to sustain yourself and someone steals your produce, you're back to fucked.