Chris is a philosophical thinker who strives to put his grand thoughts into action. Much like Henry David Thoreau (one of Chris's idols), McCandless tries to make the idealized life of "simplicity, simplicity, simplicity" a concrete reality. Much like a transcendentalist, Chris rejects the materialism that consumes so many of the other people he witnesses and desires to live an honest life closer to nature and close to God. However, Chris’s idealism proves to be his downfall as he ventures into the Alaskan wilderness completely unprepared for his adventure in terms of equipment, knowledge, and experience. Alaska proves to be more challenging than he anticipates and, ultimately, McCandless’s vision proves to be unsustainable.
I have heard it said and seen it written that McCandless was a visionary because he had predicted his own death at an early age. I have not seen this substantiated.
Instead I would say the part that made him a visionary was his need to return to nature and to find an eco-friendly way to live. Had he been alive today he would not be surprised to see the one room homes from recycled materials that are being made or other people's exodus into the wild.
Chis was just too young and foolish to make the trip without the necessary provisions. He was a deep thinker and yet he did not think deep enough to take along a map. He had cheated death once when he had nearly died in the desert. He may have thought that mortality was his just because of his youth.