Let's just hope they got the right bear
I was about to blog about this, when I saw that Hank Fox said it better than I could.
Still, something is strange about how that bear behaved--it's uncharacteristic of black bears to attack like that. I've heard speculation about rabies, but until the right bear is caught and tested, we can't know. As much as I'm against killing bears for their gall bladders, or "sport", or to get their cubs for the pet trade, I would--with sadness--support the euthanizing of a bear that acted this aggressively, killing a child and seriously wounding her mother and brother.
But killing a black bear in the hope that it's the right one--I just don't get that. Why it can't be caught, confined, and tested in order to make sure they have the right one before they euthanize it--that seems to me the sensible way to proceed.
The only reason I can think of for killing it so quickly is that they want to examine its brain right away for rabies, in case the mother and son have to undergo the immunization series. But even so, the information value from test results on the brain of a bear that may or may not have been the attacking bear is dubious. I still don't see the value of killing the bear before it was positively identified.