There's two (or more) sides to everything. The people who own the island have the legal right to kick him out. I get your perspective but if he really wants to get back to nature he should find a place where he is welcome to do so.
EDIT: For all the people asking about the details of the property owners asking him to leave, read the article linked in the next top level comment by doall.
I made brief comment on what I believe the other side of the story would be; he was sick (suspected flue) and modern medicine could heal him. In most cases I would consider that a moral imperative, as in "it is wrong if you don't do it." But according to the information presented in this article, healing an 82 year old man of the flu is not assuring him any quality of life. Consider it a "Do Not Resuscitate" order. Plenty of elderly have DNRs and have made their wishes clear; they want to die at home.
edit: article posted by doall apparently explaining he was attracting unwanted tourism to what is private property, it's in Japanese: https://www.dailyshincho.jp/article/2015/12090710/?all=1
https://en.wikipedia.org/wiki/Adverse_possession#Hostile_pos...
and
https://en.wikipedia.org/wiki/Adverse_possession#Exclusive_u...
How did you discover Mr. Nagasaki has a mental ailment?
Still doesn't explain how we, or ebbv at least-knows the gentleman has a mental condition. That seems-in the absence of anything confirming so in the article-to be an incredibly uncharitable assumption because the man has chosen a lifestyle us in the 21st century would be inclined to "other"-ize for no good and justifiable reason.
Mental illness is also a real thing and a real problem, and people with serious problems who need medication often live outside the bounds of normal society. But that issue is not going to be solved here, and I think it's a distraction from the actual topic because the reality is he was on other people's property where he wasn't welcome.
Because it is.
I'm not going to play 'let's pretend' and step around how ugly your hypothetical is, "my dude".
Anybody wanting to live on your property, whatever their reasons, who you didn't invite there, is probably not gonna be ok with most people.
These places are disappearing rapidly from the map. There's very little wild country left, and at the rate economic growth is going, there probably wont be any left in several decades.
It’s cold and heartless.
Imagine some mentally ill person decides he doesn't want to be one with nature on/as your property.
Ah, and what is health? We use this term to talk about physical health (infections, disease, cancer), mental health and also habits (eating healthy, or playing video games all day isn't healthy).
This starts to get really ambiguous. You're now applying societal standards, maybe throwing a little happiness index in there ...
We don't see living alone in solitude as healthy. Yet this man claims to be find after decades, with pretty minimal human interaction. What is health? What even is his identity?
If everyone made his decisions, humanity would cease to reproduce and exist? Is that were our baseline is? Homosexuality was in the DSM as a mental health condition. We treat anorexia as a mental disorder to be treated, as we do body integrity disorder, but we support gender reassignment surgery, even though they are all forms of body dymorphism.
I ask again, what is health?
https://leadingpersonality.files.wordpress.com/2013/09/avera...
https://leadingpersonality.wordpress.com/2013/09/30/average-...
There are evolutionary reasons for preferring averages. And the further you deviate from average behavior, the bigger the risk you run.
For example, if you lived in the middle ages and you were a radical atheist, no doubt that under that system of education and propaganda, you would have been deemed by that society to be "mentally ill" (or similar contemporary equivalent).
The charge of "mental illness" or psychological pathology in general, has throughout history been weaponized to isolate and/or suppress politically incorrect or heretical ideas that run totally counter to the prevailing world-views.
What property? It's an island in the middle of nowhere. Nobody owns jack squat.
Humans are so arrogant.
Have a good think about how that death will actually go down. This isn't falling asleep in a field of flowers. Say you have a stroke. Then follows days, weeks, of confusion and fear as you rot away on the ground. Or say you fall and break a bone. That's weeks of pain as you wait for the infection to kill you. On anywhere other than an island a predator would eventually come along to quicken the inevitable.
He may come down with any illness or condition that causes him to change his mind at any point, but no longer in a condition to do anything about it. There are certain conditions that modern civilization makes coping with considerably easier, and it’s plausible that he would chose that over his current surroundings, but no longer able to change his surroundings.
That’s the question that keeps coming to my mind.