Yea, it's not that the bears will start to see people AS food, but they can learn to associate people with food. When that happens, they begin to seek out humans rather than trying to avoid humans. When that happens, they become a danger to humans and the bear will then be put down.
This is also why you don't start a bear encounter by throwing food at the bear.
You can read the official "instructions" on dealing with a black bear encounter from the
Great Smoky Mountains National Park Web Page.
But it basically comes down to this:
If you see a bear, the moment the bear detects your presence (usually before you detect his) he will already be running away from you.
If the bear does not run away, you should start by making loud noises to try to scare the bear away.
If the bear has already learned to associate people with food and starts to approach you, try to move away, retreat to higher ground (make yourself look as large and as threatening as possible) and throw rocks at the bear.
Only if throwing rocks still has not deterred the bear and he continues to approach you, THEN you should try to separate yourself from your food.
If the bear continues to approach you, the bear might see you AS food (rare but has happened) and you will need to fight the bear with all your might. Keep in mind that you don't have to be stronger then the bear, you just have to put up enough of a fight that the bear decides you are not worth it.
Over the years, I would guess that I have had about 20 bears encounters in GSMNP. About 40% of the time, the bear was far enough away that it ignored me. About 40% of the time, the bear ran as soon as it detected my presence. Once a bear approached me while on a lunch break at a shelter. One shout was enough to scare the bear off. The only time I've encountered a bear that didn't run off with shouting, it had learned that backpacks contain food (it has stolen a back pack out of a shelter just a few nights earlier). Fortunately our packs were already hung on the bear cables provided at GSMNP shelters and camp sites, and the bear only paid attention to our packs on the bear cables and not us throwing rocks at it. Once it realized it wasn't going to get the packs from the bear cables, it left.
Given the number of bear encounters I've had, I would say there must be thousands of bear encounters in the GSMNP each year. In about the last 20 years, there's only been one death and a hand full of serious injuries in GSMNP due to bears. When you consider that is what is happening in just the National park (where you have a relatively large concentration of people and bears), you're even less likely to have a "bad" bear encounter over the rest of the trail where the density of people and bears is smaller.