Personally? I think violence, and threats of it, don't ever solve anything.
The number one rule of a civilised society could well be "don't touch".
There are very few justifications for violent behaviour, but people behave in violent ways all the time, and male violence against women ~ and against other men ~ is part of the cultural baggage of western society.
It's hard to say how long people should put up with abuse. Most people who have been abused wish the abuse would stop, but are often confused, upset and in shock. They aren't thinking clearly and their responses are skewed by their experience.
Most people in stress situations don't think well, really, and very often people stay well beyond when they *should* or when it would be appropriate, holding out hope that the abuser will change and become the person they used to love, or that the 'honeymoon' periods between abuse might be permanent this time.
People who are abused know something many of us don't recognise about abusers ~ that they are often acting out of grief and pain that isn't expressed otherwise. Where we see a thug and a bully, they often see the vulnerable spirit.
Who sees more clearly ~ both views might be correct, but the abused person fails to realise that by staying, they are not forcing the abuser to confront their behaviour and try to change.
It's a complex and terrifying dynamic, and very few of us could say with real truth that they would *never* behave in this and that way ~ not unless they've been there.
How much *should* any of us be prepared to tolerate? None ~ we should never be willing to tolerate abuse. But how much DO we tolerate ... that's the question with a human face.
It's also worth remembering that the period just after leaving a relationship is a very dangerous time for women especially ~ that is when they are statistically at most risk of being killed or permanently injured by the abuser. That message isn't lost on lots of abuse victims.
Very thought provoking question, and certainly better than the once a day "When is it ok for guys to hit women" and "why can't I hit girls" questions. After a while, it seems appropriate to change the wording a little ~ and watch the fur fly :-)