So let me understand this.

A POLICE OFFICER lets his dog out unattended, the dog wanders a quarter of a mile from the officer's home and you people are mad at the guy with the GUN because he felt the need to defend his child from a dog he didn't recognize that was in his yard!?!

Just for fun - would you be mad if the neighbor owned a large, powerful dog that got loose and wandered into the officer's yard and the officer shot it? Or would the neighbor still be an idiot - but this time because he left his dog out unattended?