I think the argument boils whether Chris was unprepared (mentally and equipment-wise) to go into the Alaskan wilderness. If you read "Into the Wild", and the newer "Back to the Wild" book which has entries from his diary and photos from his cameras, I think it's clear Chris was very prepared mentally - he knew exactly what he was trying to do, and he knew exactly how dangerous it was. He spent months working out, climbing mountains with his heavy pack, and researching wild edible berries and game in preparation for what he wanted to do. This shows he had a clear mind going in.
So essentially, he was trying to do something dangerous, with the minimum amount of gear possible.
This is no different from the countless people that attempt to climb Everest or K2 without oxygen and perish in the attempt. Those people are not considered dumb asses. Neither are the countless thousands and thousands that perish getting out there and pushing themselves as best as they can.
A person's level of preparedness for any life adventure is clearly their own choosing. Who are we to say that someone was foolish for attempting to push the boundaries of what they thought they were capable of?
Even worse, if someone were to be the first to summit some mountain or other without oxygen, they would be hailed a hero. If they died, they'd be a dumb ass. The outcome should not have any baring on if they were "prepared enough" or not - only they can make that choice for themselves.
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As a side note, have you even spent any time in Alaska or with Alaskans? I live up here. If you were to go more than 10 yards from a highway and didn't have a quad, rifle, chainsaw, axe, saw, three pairs of boots, sixteen gloves, spare everything, spare gasoline, 300lb wall tent & stove, sat phone and a spot satellite messenger and you so much as broke a fingernail, Alaskans would very quickly point out you're a complete dumb-ass for being so horribly unprepared. Even worse, you go by yourself.