The issue here is not that the dog has never bitten anyone. The issue is not wether the dog was "good" or "bad".  The issue is that the person who shot the dog thought the dog was attacking him.

If the owner of the dog would have just kept the dog restrained then this whole thing could have been avoided.

I cannot honestly say what I would have done, I was not there and do not know any of the parties involved. What I do know is that a large dog running at you at full speed with his teeth bared (just protercting his turf) can be pretty frightening, and in the split second of decision making time this person decided to draw his weapon and fire.

We should be focusing our anger at the owner that chose, and yes it is a choice not to restrain his dog, which is ultimatly the root cause of this dogs death.