I understand this sentiment completely. I didn't deal with it in the same manner you did, but my dearest friend....I mean, she's practically a sister to me, was involved in a very abusive relationship a few years back. This is someone I've known 20 years of my life. I would see her daily with bruises, scrapes, cuts, broken bones.....it killed me. I went to the cops, I saw a lawyer, I dragged her into court to file a restraining order and none of it worked. She was terrified for her life and I didn't care much if he came after me for getting involved.....knowing she was safe would have been worth it in my eyes. If someone had handed me a gun and told me to shoot the bastard and I'd walk away from it scot free, I would have done it in a New York minute. There are some abhorrent strains of humanity on this planet that the rest of us shouldn't have to deal with. I'm not saying I would have killed him, but I would have made it so he couldn't do much of anything for a very long time.
One day she called me from the hospital and told me to come pick her up. So I drive over there and as I'm getting her into the car, she looks at me and asks me if it would better off if he did kill her. The day you hear your best friend of (at that time) 18 years say something like that to you is a day I hope none of you ever have to deal with.