I'm having a little trouble with this one.
First, let me say the law can be an ass. If the law and law-givers presume to be able to control human reactions, they're being unrealistic. If a man, having survived a robbery attempt, goes into a towering rage and shoots the robber "too much", I think the law is asking for trouble. We're talking about some very powerful impulses here--survival itself, being on the receiving end of a threat to life, and so forth. It doesn't get much more emotionally charged than that.
To have that thrust upon a person during his normal day-to-day mundane life, and then expect him to not have a very powerful reaction is nuts. Failure to recognize that those powerful reactions can come in more than one form--overmastering fear, rage, grief-- would be just a sub-category of the same nuttiness. Add that not all people who are entitled to defend themselves have the training about lethal force legalities like police or some of us. Meaning, they may not know they must master that rage or face legal problems. Its one thing to expect trained cops who face violence or the threat of violence every day to respond properly as trained professionals...
With all that said, the problem I'm having with this one is that it does seem a bit cold blooded. The video only played once for me. But, what I caught was that the guy didn't seem all that enraged. No foot stomping, no yelling at the ceiling to let off anger, that sort of thing. Just goes off camera, then comes back and shoots several times, then turns and walks away.
Hmmmm. It does occur to me that one can be in a rage without manifestations that would show on video. No law of human emotion says overmastering rage has to include certain actions that would show up on video.