Moral of the story is don't get in the middle of domestics. Cops can tell you, the spouse you save will turn around and testify that you where the aggressive one and that the abuser was just defending themselves.
Well, truth is, just be careful about how you do it. The don't get involved advice has it's own problems and leads to things like the crowed of cowards that stood by and watched a pitbull kill a 3 year old (I have broken up two pitbulls fighting while a dozen people just stood around and yelled, so yes, I will say for a fact I would take on one pit bare handed to save a child and as such have no qualms calling those who would not cowards).
Now I'm just rambling before work, but I agree with your intended moral, plenty of people can have multiple holes in them and still function. A wise man assumes any opponent will be such a person and plans accordingly.