I am very sad to say, sometimes you can do everything right and still end up losing.
First of all, I am all for holding officers accountable. If they screw up, they should be held to a high standard. Second, "acquitted" does not mean "not guilty." It means the prosecutor did not prove to the jury that the accused was guilty of the charges beyond a reasonable doubt. O.J. Simpson was acquitted of the murders of two people, however it is pretty clear to anyone with a modicum of common sense that he did it.
Philando Castile did everything he was supposed to. He did everything right as it was taught to him by law enforcement and the NRA. Identify that you are legally armed to a police officer on initial contact. Make no movements without being told. Follow all commands. What makes this a tragedy was a nervous officer feared for his life and shot. That does not make it good, right or justified. It just is. All it does is makes this a tragedy for all people involved and their families.
I have seen a lot of backlash against the NRA because they didn't "immediately respond" about Castile's death, like they did about the killing of five Dallas police officers by a sniper a day or two afterwards. The difference is that in the sniper shooting, there is very little ambiguity about the circumstances, and there was a lot of ambiguity about Castile's death. An investigation needed to be performed in the matter of Castile's death to determine circumstances and context.
Just to show you how quickly things can go south during a traffic stop, This video was an officer from the Opelika, AL police department shooting an airman involved in a minor traffic incident.
At 32 seconds, the airman opens the door to his vehicle. At 35 seconds, the officer sees something in the airman's hands and commands, "Lemme see your hands!" At 37 seconds, the officer commands "Lemme see your hands!" a second time and two shots are fired. At this point the airman goes down. Think about this, two seconds between the first command and shots fired. It is obvious that the airman has something in his hands. A later, second and third look shows it to obviously be a wallet. At first look though, you can't be 100% sure and that kind of "not sure" can easily mean "dead officer."
Here is a second video to prove how deadly two seconds can be to a police officer: