Rather than questioning if the knife wielding person needed to be shot dead, perhaps it would be more constructive to suggest a reasonable alternative to not shooting him. I’d personally prefer that he not be killed — it would be valuable to interrogate the bastard to see what led him to attack several innocents with deadly force — but approaching a person who has demonstrated homicidal intent, and restraining him from endangering any other innocents is dangerous to say the least. Remember that suicidal killers like this one have been known to blow themselves up after being wounded while police and medics approach them to render first aid. Current UK and Israeli policy in dealing with terrorists of this sort is to administer multiple headshots to keep them from tripping any possible explosive device.
Remember the Colombine massacre? There police established a perimeter and waited for SWAT. The two killers used this time to murder more people. Since then, police policy has shifted more to protect innocents than to protect themselves. A more than reasonable shift IMHO.
I’m no fan of the police myself. Their job is to protect us, and when some of them do exactly that, I’m interested in hearing how it could be done better, but not on a critical level. When they rob, kill, and brutalize citizens, like so many of them are doing today, I’m more than happy to support maximum punishment.