I get the feeling most people, on viewing this film, would have one of two reactions - perhaps depending on your politics or world-view. One is, "What a brave/noble man!", for standing up for what he believed in so strongly, even unto death. The other is, "What an impossibly stupid man!", for ignoring and taunting the dangers he knew so well in his head. The strange thing is, I can see both viewpoints - and it reminds me of how my own ideals don't mesh with reality. He's more like us than most of us will admit, just to an extreme.
Treadwell fashioned himself as a preservationist, standing up for the bears who could not speak for themselves. He did teach many children and others about their plight, which is undoubtedly helpful. Problem is, most of the bears he 'protected' were in national parks and not in much danger from humans, aside from necessary and controlled huntings. He became more of a Don Quixote figure, more tragicomic than effective. Most of the experts in the movie believed he may have done more harm than good.
The bears became his family/friends, or so he thought. I actually thought he had a bit of the right idea early on - if you are going to try to stand up to them, intimidation/confidence would be important. Perhaps the bears sensed that he had that confidence, and that's why he survived so long. Perhaps it's like one of the contributors said, and they thought he was 'brain damaged' and not worth the trouble, or perhaps he got lucky. Probably a combination.
And I find that combination is something of a parallel to our coexisting/struggling with nature, something most environmentalists don't acknowledge. Nature is beautiful, but harsh. You only see the bleakness and pain, and you'll miss the wonders there, like the awesome foxes that befriend Timothy. At the same time, to romanticize it is to do a disservice to truth. No matter how much Treadwell loved that bear, it remained hungry, and he was a convenient food. Keeping the balance in your thinking is the key, and the difficulty.