@lillycoyote, did you think I was attacking anthropologists? Certainly not. I’m just saying that their experiences answer the “voluntarily assuming” part of the question details. There have also been movies that based fictional stories on such narratives. I can’t think of any titles at the moment.
One movie that does fit the bill, I think, is The Emerald Forest.
How about settlers who went from the highest civilizations of their time to the relatively primitive environments of the colonies? Even if they were not living directly among native peoples, such as the Native Americans on the North American continent, they were certainly not enjoying the lifestyle they had left back home in, say, England or France. Terrence Malick’s The New World explores this contrast. As a matter of fact, the beginning of his The Thin Red Line also focuses on a character who has chosen to abandon his former life in favor of a tropical paradise.
Missionary stories such as Hawaii also treat this theme.