You say using evil to stop evil is wrong but what do you know of evil? I'd like to know what you do for a living. It is probably an office job or something like that. Something safe where you are not questioned or put into life or death situations.
I am a police officer in a bad city. I have to deal with use of force often whether it be all out fighting or just getting someone in cuffs that's resisting. I have drove 120 MPH towards houses I may get killed in or have to kill in. I have responded to calls where people are getting robbed at gunpoint, where people are getting kidnapped and where houses are getting broken into. You know nothing of evil if you stand by your opinion on what the Bible teaches.
You say you can't shoot someone out of love. That is a horrible lie.
If someone pulls a gun on me and I shoot them, I am shooting them out of love. Love for my wife and family. If a drug addict addict is going to slit a child's throat and I shoot him, I'm doing it out of love for the child.
I entirely agree that there are difficult questions here. But we must remember that our first obligation is obedience to the kingdom of God model that Jesus sets for us. That may well mean that we forfeit our lives. Hopefully not, but it certainly is a possiblity. Narrow is the way.
I've never struck someone out of hatred. I don't want to hurt anyone but make no mistake about it, I am going home at the end of the day. If that means putting a brick through someones head to stay alive I will do it.