Bad situation and bad judgement in that video. The guy was high on PCP and armed, but he is clearly angling away from the officers. The guy had a knife so the officers were in their rights to respond with lethal force if the guy posed an imminent threat. Dude was clearly walking away though so no imminent threat. Officers should have tazed him since he was walking away, but that's not what happened.
"We are all born ignorant, but one must work hard to remain stupid." ~ Benjamin Franklin