They killed it because it chewed someone! According to that story, they found the bear in another camping area, so despite being blasted with an air horn and pepper spray she still didn't think that people were all that scary. She sounds like a hungry bear, and she was associating people with food, and possibly as food.
There are programs that try to educate problem bears by chasing with dogs and hitting them with 12 guage bean-bag rounds. Last I heard that was working well. But those were bears that had stopped short of biting anyone.
Just think of the storm that would errupt if someone (say a child who can't punch very hard) was killed by a bear that was known to have attacked others, but had just been left alone?