I totally grasp the financial aspects of avoiding rent on a flat. And gas, electricity, cable TV, landline, water and sewer bills, etc. I see people do that here in Alaska by living, well, like it's 100 years ago. Log cabin or plywood shack, maybe 12 feet x 16 feet. Heat with wood, haul water from the General Store. Score lots of fish in the summer, go clamming at low tide, pick berries, etc. As such, $3,000 to $8,000 for a few remote acres, and $1,000 of building materials and you have NO overhead compared to even the cheapest apartment ($500/month?) + phone, power, heat, etc = $700-$800/month.
Some things I saw help make that lifestyle work: Be a great worker. Someone who shows up, does good work, and gets along with everyone. The best casual labor I had working on my house was a guy lived in a treehouse. Yes, a treehouse, in Alaska, year-round. There were months when we'd be fighting over who got to hire Gus. Whereas other hippie dog mushers, I'd only hire for certain low-skill, highly supervised activities.
Another is be a good guest. A pleasant conversation and helping with the dishes gets you invited back. By unspoken agreement, the smokey, sweaty, off-the-grid dinner guest arrives 30 minutes early, goes to your bathroom, takes a shower, changes into his last clean set of clothes, throws everything else in the washer and comes down for dinner. Sometime during the entree course, he moves the clothes into the dryer. After dessert, his laundry is done and really, we preferred him in his washed and changed state than how he first arrived at the house.
Managing a computer store in Berkeley in the 1980's, I had an employee who lived in his van. Took meals and showers a student housing co-op. A few more showers and more attention to his wardrobe would have made it more viable.
I've long thought that there are times I only want a bed with a bathroom down the hall. A 5' x 10' room would suffice and be so much cheaper, greener and lower-impact than a standard 300 - 400 square foot hotel room. New Yorkers are greener than most anyone else because they have small housing units, share 5 of the 6 walls (hence reduced loss of heat or A/C), all take public transit and few have cars. Going to my proposed coffin-like housing could reduce that even further.
I suspect you contribute to civil society in another way: by being an upstanding citizen frequenting parks, late-night cafes, and bookstores, you keep those places safer than if few people were around. American cities can be so devoid of decent people after work and dinner hours. Again, NY "the city that never sleeps" is safer because of average people being around at all hours. Most people would be home, watching the TV for hours a day, but you're out and about interacting with or at least seeing and being seen by other people.