I've fed and housed people for decades, provided transportation, donated skills, and rehabilitated wild lands. The people who receive the benefits from that didn't do anything to get them. They simply needed them. If I have extra and you need some, you can have some. Simple as.
Most people want to contribute, pay it forward, or give in their own way. Almost no one wants to do nothing to give back. (Usually, the people who do are the people who have been stepped on their whole lives, and by receiving aid it buys them a chance to rest. Once they've rested, they tend to help out where they can.)
I guess I'm going to believe my decades of lived experience with mutual aid over some stranger telling me things I've observed sustaining themselves are impossible.
OK, that's great and respectable.
But you don't address the core problem which is "How do you handle the people faking (often even faking out themselves!) the need for selfish gain?" and "How do you handle the people who see others lying for gain, and they themselves convert from the helpers to the helped"?
Most people just sweep this under the rug, because it is an obvious and fatal flaw in the system. It's also ideologically uncomfortable that powerless people (have nots) can be just as shitty and morally awry as powerful people (haves).
The world shouldn't be a place devoid of charity and helping out those who need it. In fact it's critical to maximizing society for everyone. But building a system with those ideals being the center pillar is backwards, because it puts the rewards before the work. A side spoke of support? Sure. But the center framework? Doesn't work, and there are ample examples, because every kid votes to get cookies first with the promise of eating their veggies later.