true.... to a point. there are other ways , people are trained in how to disarm or deflect a knife attack.  and really how many people know how to use a knife? a pregnant woman? 
Or,  how about bean bag her until she drops the knife? it's risky for her and the baby, but at least there is a good chance she is alive. why not a trank dart? if you can hit her with a bullet you can hit her with a chill dose. again risky, but a good chance of being alive.
  i'm saying there are more ways to stop someone that putting a bullet in their heart. what happened to all those less lethal weapons? i never hear of them being used. cops are under a ton of stress and have become targets themselves....i think  brought on by their harsh treatment of people. they shoot a lot of people anymore. and i think it's great that there are cameras. to see for yourself how something comes down is invaluable. one video says a million words.