In my regular discussions with people, as people run out of logical approaches to an argument, I frequently come across the argument:
...but if you were stuck on a desert island, would you...
The implication being that if you place the argument in a scenario that is extreme and unrealistic, and that argument fails in that scenario, the argument is invalid in the more frequent and realistic scenario.
My searches on Google seem to suggest this is called a Robinson Crusoe fallacy which seems apt but not formal.
Is Robinson Crusoe the correct term for this fallacy or is there a better one?