We shouldn't expect the same things to work for both. There is room for your own judgment in police work, within parameters. Or, obviously, should be given the seriousness of the issue of distrust between many people and their police forces.
The officers involved showed excellent judgement by giving repeated warnings to the assailant. They did not fire until he charged them. The fact that he literally fell at their feet tells me they almost waited too long.
I, for one, don't want them to take a knife in the guts to satisfy people like you. I want them to go home to their families in the same condition they were when they put on the uniform.
It was a completely justifiable shooting. You just need to get over it.