Really, I dont know why there is such a controversy over this. Both "sides" both don't want cops to be killers. Both "sides" don't want young black men killed. The only real controversy is what really happened. And the fact of the matter is, is that only a few people really know.
There are basically two possibilities. 1.The cop was racist, hates blacks, and had a vendetta. Decided he didn't like the kid, and thought "hey, i'm gonna murder this kid". 2. The cop was attacked, felt threatened, and did what his training taught him, which is shoot to kill basically. They don't teach shoot to incapacitate.
Any outcome sucks balls. Sucks total balls. We have a dead human being, and a police officer whose life and career is forever marred. I think most people look at this and decide based off what they know, and life experiences to come to a conclusion. But the thing is, none of us really know what happened. NONE of us. We are all basically picking what we logically think happened. People who tend to think that most cops have a chip on their shoulder and are out for blood obviously think scenario number one is most likely. People who tend to think of cops as normal people, most of whom want to do right, want to think that the cop wouldn't just murder someone unnecessarily.
Since none of us know what really happened, we are all really just saying what we think happened. The type of environment we are raised in impacts this thought process dramatically.