You should never kill an animal out of revenge. The animal lives in the moment and unless consequences are delt within seconds of the animal's actions, it will not relate the punishment with the incident. The frame of mind "Bear attacks human, human kills bear" seems pretty primitive. The bear recognized a threat, protected her cubs and ran off. No need to run after her and put her down just for doing her job.

If there as a renegade bear out mauling hikers, then it would need to be handled. This situation was simply an accident. You startle a bear and you're going to face some serious consequences.

I don't believe the sting ray that killed Irwin was offed. And I'm pretty sure the bear who killed Treadwell is still wandering around.

This is just what happens when you get too close to wild life. Things get crazy.