One problem is that it is hard to prove self defense when the abuse that a person suffers is extended over a long period of time. It is harder to establish that the abuse is life-threatening.
I was abused so I became an abuser? If that is the reality that a person is forced to endure for 18 years and longer, then what exactly is wrong with that plea? The person failed to make the Herculean effort that it takes some people to overcome such abuse? The person failed? Oh, he's not a machine, he can be held responsible, all that GARBAGE?
Learn to feel lucky for everyone who does come to some kind of accommodation. They are going above and beyond what they are rightly responsible for. So it may seem that almost everyone who goes through this manages, but I have other opinions. Instead of one person attacking one other person and injuring or killing them, the result is often a wave of mass murder committed by one nation against another, and they make it a holy cow instead of what it is, a thing that makes the term "obscenity" far less than enough to cover it.