I think a lot of the national park bear problems (besides hordes of tourists either actually feeding bears or at least leaving their food where the bears can get it) is that there is no hunting allowed. In national forests, where bears are hunted, they are generally quite shy. The exception, of course, is where they have gotten hold of food and realize that humans have food with them. This often happens around car campgrounds, but it can also happen in the wilderness. I'm sure I cited the case two years ago where some idiots went off for the day leaving an slab of bacon in their tent. Of course the bear followed his nose into the tent and learned that tents = bacon! The next group in the area was a trail maintenance crew; I understand they lost a couple of tents to the bear who was of course looking for more bacon. That's why, IMHO, even in areas where bears aren't (yet) an issue, we should protect our food. We don't want to train any more bears to go after human food! It's not just to protect our food; it's to protect the food of the hikers that come after us and especially to protect the bears--"habituated" bears invariably end up being shot.

Jim is correct that we don't need to carry bear spray for black bears in the US (although I understand there have been some problems with black bear in Canada). Grizz are, of course, another story!

It's interesting that so many people worry about wild animals when by far the biggest hazards to hikers are hypothermia, falls and auto accidents driving to/from the trailhead. The chances of getting killed or hurt by wildlife are quite minute, unless you do something utterly stupid. That's why the rare instances when it does happen make headline news (the "man bites dog" thing).