There is a gang mentality that has taken over modern policing. You see it all the time on shows like COPS... and it can resemble mob 'justice'.
Police descend on situations with massive over-reaction.. like a pack of wolves in some cases for situations that could be better handled with some tact. The intention is to utterly disorient and immobilize the individual.. which in as many situations as not causes a reaction as the subject becomes confused, enraged and humiliated... remember the Robert Dziekański tasering death at Vancouver International Airport.
Good policing used to involve some artistry, flexibility and strategy to defuse potentially dangerous confrontations.. and certainly commensurate force. That's not the playbook now.. it is overwhelming force and an assumption that the officers lives are in imminent danger even when there is no basis for that.
Now a man with a knife is a definite threat. But given the distance, the weapon, the bulletproof vests on the police, his not harming of other individuals and the character of a clearly mentally unstable individual.. this could have been handled with less than deadly force.
Tackling or Tasers OR shooting to wound, which has been removed from the police protocols.. if you shoot now, you shoot to kill.. could have been used.
I'd refer you to the situation in Montreal in the last couple of days where a man (likely on crack) went on a rampage on the street, beating to death an elderly woman.. but was brought under control with less than lethal force... that's good policing. What the Toronto police did was target practice with live ammo on a live target.
There are good police.. but there are some who just want to put a notch on their pistol grip.