Tamir Rice was a tragedy but it absolutely was a just and good shooting.
The officer didn’t have the luxury of 20 / 20 hindsight. So if your going to be fair you can only judge him based on what he knew and what he knew was that someone was waving a gun around in park and that it was a shooting about to happen. He wasn’t told that the caller thought it was a fake. He wasn’t driving so he couldn’t control where the car stopped. He couldn’t control Tamir Rice’s actions as he jumped up and started pulling the gun on him. All he could control was how he and any sane person would react upon arriving at a man with a gun call and then suddenly having that person with the gun right in front of you and drawing that gun.