wherestheham,
I am sorry that I was not there for your wife and child. One of the greatest burdens LEOs must bear is having to look into the eyes of the victim and and see them silently asking "You're here now, but where were you when I needed you. How could you let this happen to me?" Each victim haunts us.
I agree with everything you said in your post. But I would like to say that it is my gut feeling, that of the people who post here and say they would choose not to intervene, very, very few would have stood by and watched your wife and child get beaten while they did nothing. I believe most, if not all, would have done something to help.
Again, this is why the "sheepdog" analogy resonates so strongly. But you know all that now, so much better than most. This is not an academic exercise for you. For you and your family, it is reality in all its bitter, ugly and brutal truth.
I hope you have decided to train yourself to be that sheep dog for not only your family, but the next family. As I'm sure you know, if you make that commitment, you must train, and train in many different disciplines than we have time to cover here. Seek professional instruction. Prepare yourself, mentally and physically, so that if that terrible moment comes, you will not have to hesitate, you will only have to do what you know is lawful and right. Ultimately, that is all any of us can do. God be with you.
My deepest respect to you and your family,
DarkSoldier