If you stop and think, you just allowed yourself to get attacked. I know I'm not the fastest guy around, but a dog is pretty damn fast and if you give a dog a second, it can close a sizeable distance.
Stop and think about reality before knee-jerk emotional responses.
Oh please. I'm not the one who needs to stop and think, the cop needed to do that. You don't just go around with a gun in a neighborhood and shoot at anything that moves. You need to think and assess the situation, including the threat. Considering that the dog was still IN THE YARD and that the officer was OUTSIDE THE YARD, I have a difficult time thinking that the officer didn't have time to take other action, including waiting or backing up. If the dog actually comes out of the yard, then yes, it's unrestrained and I can see taking action to protect himself from the dog.
I wasn't there, so I don't know. We're all speculating based on the information provided, and based on what I've read, I think the action was very inappropriate and I don't think I'd be confident with such a trigger happy (or incompetent) individual walking my neighborhood armed and ready to blast anything that might move.