And that's a very American viewpoint.  The ubiquity of guns, the casual discussions of ending someone's life...  it's part of a bigger problem outside he scope of the discussions.  Practically speaking, though, to shoot him in the face, you would have to get him to turn around, though since he was running away.
Reaching for an officer's weapon is stupid.  It was a lethal mistake by someone who was impaired and panicked, probably because he was on probation and this arrest would have sent him back to prison.
In the article, they do give the officer the benefit of the doubt that, in the heat of the moment, he may not have processed the fact that the Taser had been fired already and could not be used again.  But this officer had previous citations for use of excessive force and he made a very bad call on this one.  
He had the guy's license.  He had the guy's car.  The guy could have run but eventually, he was going to be captured and sent to jail.  Instead, he's dead.  The public will accept officers killing a citizen but there has to be a really good reason.  In this case, the use of force didn't match the risk to the officers or the public and I'm not sure a jury is going to let him off.