I'll accept that introducing humans to any ecosystem is going to change it in one way or another. I think there's a pretty big [citation needed] over "ruin it".
If they are aiming for a similar impact level to, say, a national park then that's a lot better than it being approved for broader development.
As for the easement, in exchange for those things they "eliminate most or all development potential in order to protect some conservation value(s) of the property that provides a significant public benefit." (from that link.)
Seems like one would need to look at the specific terms of the Rabbit Island easement in order to further quantify any claims.
I'm familiar with an area a bit further west, and while overall the economy is still very depressed and the population remains sparse, prime properties (lakefront, near certain amenities) are being snapped up -- often by moneyed interests from downstate or out of state.
What these fellows propose and appear to be executing, sounds much more conservative (in the a-political sense) than some alternatives I can imagine. And it appears that the State had no interest in acquiring the property, nor whichever county that is (probably cash-strapped and not eager to take on the management and liability).
Artists retreats are also a bit of an established tradition. There's one further west, at Porcupine Mountain Wilderness State Park. And they seem to dot the upper peninsula (UP) and northern Wisconsin.
FYI: benefits of easement - http://www.michbar.org/journal/article.cfm?articleID=95&...
•a federal income tax deduction for the value of the easement
•the right to subtract the value of the easement from a decedent’s estate in calculating federal gift or estate taxes
•the right to exclude 40 percent of the remainder value of land subject to the easement in calculating federal estate taxes