Your are not arguing against the parent comment, right?

Because when somebody attacks you with a knife, drawing a gun oftentimes will not even be an effective defense. But if that is all that's available to you, it's only reasonable to give it a try. You should shoot multiple times or empty the whole magazine though and yes, that's generally justified by the law if that's what it takes to stop the attack.

The exact thing has happened to police man and woman and yes, they get trained to shoot multiple times to defend themselves. Was an outcry in media a few times because people don't understand the situation those people were put into.

I'm saying that when you use a gun against an attacker with a knife you will end up before a judge as the defendant and not as the victim. The court will decide if using the gun in this specific case was necessary (notwendig) and appropriate (geboten). Only if it was both will you go unpunished.