Answering this earnestly with the assumption that the final paragraph is in good faith. And stating for the record that the below summarizes my attempt to imagine the best we
could do with the ingredients we have. If I were building a world out of whole cloth, my ambition would be grander.
To be clear about the whole Amish/uncontacted tribe/et all scenarios -- the point I intended (but perhaps did not make) was that I'm not especially interested in what hypothetical people think about anything. They don't exist. Every single real world example suffers from problems in the vein of those present with the Amish example. Kowtowing to the needs of hypothetical people has, historically, caused far greater harm than good.
To your questions -- my beliefs in this arena largely boil down to this: each member of a community has an inherent responsibility to contribute that which they are able, both in terms of ability and in terms of resources. No more, but also no less.
The reason this responsibility exists is that every member's success is inextricably linked with their community -- because success (beyond sheer survival) is measured by community. One cannot exist without the other -- and a high tide lifts all boats. In our current global system, living outside of any community is, practically, impossible -- so the responsibility is inherent.
Homeless are not exempt, but consideration would be made for the distinction between folks of comfortable means versus those living on a day-by-day basis. One group has resources and ability in excess of their needs. Another group lacks the resources to sustain ability. To lift them up is to lift the community. Sure some folks would refuse to change in accordance with societal standards -- but a lot less than you might expect, once the barriers of social shame, inefficient and needlessly cruel bureaucracy, and infantilization are removed. And yes, were we to implement this tomorrow, the above wouldn't happen overnight. The point is consistency and transparency in service of making everyone understand that they the individual is part of a greater whole.
Which is to say: I believe that the more one contributes to a community, the more the community becomes what it's meant to be: a collection of disparate people making up a symbiotic human ecosystem.
Obviously this system assumes folks acting in good faith, which feels lacking at the moment. But I'm hardly alone in believing that lack is due in large part to the current lack of everyone having skin the game, due to policies pushing problems back and forth, costing everyone money and attention, and accomplishing nothing but creating frustrated factions.
Hope that clarifies my position!