Do you understand that the majority of men that fought and killed the Nazis in WW2 were Christian?
Think about how your golden rule applies to reality. If we had taken this approach, the Nazis would have likely won the war and European Jews wouldn't exist today.
I have to wonder what you would have said to those starving in the concentration camps at the time.
"Sorry about your bad luck, but I'm not willing to get my hands dirty on your behalf. My eternal soul is on the line, you see? So you're just gonna have to suck it up."
@Debp posted a great example of the man who stopped the mass shooter. I don't know what the guy believes, but I've yet to find anyone, Christian or otherwise, that has said he was in the wrong for putting a stop to that evil.
Is it technically wrong? Sure. He murdered a man for the greater good. It's still murder, but it was for the right reasons. Namely to save the lives of others.