To be fair, handguns can be quite accurate even at a reasonable long range. I’ve regularly knocked over #3 cans at 25 meters with a Browning Hi-Power or Ruger Mark II. However, the cans weren’t moving, they certainly weren’t threatening me, and I wasn’t under stress. In a realistic defense scenerio under simulated stress, even an experienced shooter in an otherwise ideal environment is doing pretty good to get inside the 9 ring on a B27 target.
Shooting the gun out of someone’s hand, or shooting a suspect in the arm or leg is not only infeasible for a shootist of even superior ability, it’s neither safe nor inherently less harmful. For one, a shot to an isolated target like a hand or leg is less likely to hit and more likely to pass through and through, posing a hazard to bystanders, where as an accurate shot to the center torso is more likely to stop inside the torso, or at least lose enough energy to pose only a marginal hazard to someone behind. Another point is that a shot to the arm or leg is likely to do serious, permanent injury and can even easily result in death; severing the femoral artery in the leg is likely to be just as lethal as a shot to the heart.
And the fact is that a police officer, like anybody else, has no business dropping the hammer on another person unless they have a reasonable belief that this person poses a realistic threat to life or limb of the officer or others. Peace officers have a somewhat expanded set of responsibilities dictating when the use of lethal force is allowed–an officer may, for instance, decide to shoot a fleeing suspect on the basis of the suspect being armed and representing a threat to the public at large, whereas a private citizen would be generally permitted to use such force only if the suspect presented an immediate threat to a specific person or persons–but ultimately police are held to the same standard regarding the judgement to use lethal force, i.e. the perpetrator was armed or otherwise threatening, and the use of a lower level of force would have been ineffective or put the officer and the public at large at greater risk. “If you’re going to take them down, take them all the way down,” is the advice one police sergeant in a major metropolitan police force with whom I am acqainted advised his subordinants, and by that he meant that if you elect to use lethal force, don’t delude yourself that you are doing anything but; if you’ve determined that the use of a firearm is necessary, then follow through and incapacitate the suspect. Any police officer involved in any shooting will be placed on administrative leave, and if there is any question of the justification for shooting, will have to face an inquest. (He probably will, anyway, just to satisfy that the shooting was properly investigated.) Shooting someone that isn’t a threat and could have been stopped by other means is virtuely guranteed to result in a liability suit and very likely criminal reprocussions.
As far as anyone from beat officers to special tactics teams being advised to shoot the gun out of the hand of a perpetrator or whatnot, this is pure, unabashed Hollywood bullshit. Police offiers are taught to make center of mass hits, period. Look at the B27 target again; you’ll see that there’s no scoring for a head shot whatsoever. SWAT/HRT/SOCOM operators may be taught and, on isolated occasions, instructed to take head shots, but this is to disable a target that may remain a threat if not assuredly incapacitate (i.e. someone wearing body armor, or holding a hostage), and invariably done using scoped carbines or rifles, not a service-grade sidearm.