The police have carried out public executions of major criminals, such as people guilty of being Brazilian electricians in a public place, barristers having a nervous breakdown in their own home, "Irishmen" carrying loaded table legs home et al. Did any of those stop the practice of allowing gung-ho coppers to run loose on our streets with loaded firearms?
That is not a reasonable explanation of events.
Put yourself in the place of the copper holding the gun......
It is your duty to prevent loss of life and limb to everyone, including the suspect where possible. This means bottling out because you are scared or because you don't want to make a decision is not an option. It could end up with you, your mates, or an innocent passer-by dead. You could then have to pay a legal price
for failing to do your duty. Being dead makes it difficult to go home to your family at the end of a shift. Somebody else being dead because you wimped out is a mental torture that you and the dead person's loved ones will have to suffer from then on.
But judgements have to be made, often in just a second or two on information which is most likely to be incomplete and possibly factually incorrect through no fault of yours. If you know anything about use of force in violent situations then you will know that action beats reaction. Do you wait to be shot at, or for somebody else to be shot? Hmmmm... 50:50? Phone a friend?
Sometimes the only answer to a person of evil intent with a gun is a cop with a gun. An imposing presence and a righteous moral attitude a la Dixon of Dock Green just don't cut the mustard.
You will be judged on what you knew at the time, and what you should have known had you carried out your duties diligently. This includes making sure your training is up to date including knowledge of policies and procedures, and availing yourself of the latest intelligence. If you don't know this stuff and it contributes to you causing a death, then even if your motives were good you are guilty of manslaughter by reason of criminal negligence.
Suppose then you are fully genned up on everything, but somebody else has let you down by carelessness, or even a genuinely honest mistake. Eg the intelligence officer has briefed you wrong, or the observing officer makes a wrong call leading you to open fire. It is not your fault, but still you end up going through the stress of a protracted investigation, often taking years, and still you have the anguish of knowing that you took life even though it was somebody else's fault.
Re the Brazilian shot in the tube station, it is tragic. ( everything here was gleaned from the media - no secrets revealed from me, I was nothing to do with it ). I feel for both the man's family and the cop who pulled the gun. The man was misidentified as one of the offenders from the 7/7/5 terrorist massacre by an officer keeping obs on a building. The real terrorist escaped undetected dressed in female muslim garb. The armed copper pursued the man into a tube station where he vaulted a turnstile to get into a crowded area. The officer then repeatedly shot him because it was (wrongly) believed he was about to set off a suicide bomb. If a terrorist was going to set off a bomb then where better than a tube station?
Armed cops are trained to "shoot to stop", which means applying enough force to avert the danger. In what was ( wrongly ) perceived as a very high risk situation a very high level of force was considered necessary. If you were that cop in that situation, would you have waited to see what he did? If you had waited and had got it wrong, then you and a whole load of innocents would have been smeared all over the walls!
Your description of a gung ho execution is as offensive as it is factually incorrect. I take my hat off to armed coppers who have to face potential death/mutilation and/or pressure from having to deal with this sort of incident. I can't understand why they do it but am grateful they do. Without some armed police we all would be in deep s***.
[No - I have never shot anyone, but was shot a good few years ago].