If you tell someone their job is to arrest this violent & possibly-armed wacko person, then they deserve the right to defend themselves, as fleeing isn't an option they have. If a cop says "don't make any sudden movements" and wacko person starts making sudden movements, well, their fault. Cop shouldn't have to let them start shooting before defending themselves. They can always choose to do what the cop says if they're worried about their safety.

But this is IF cops are solving crimes at all. If they're not, then fire their dumb asses and just let's officialize vigilantism. Because this halfway-in-between shit isn't good for anyone. Do it or don't do it.