It really depends on your perspective. Ghandi would say that no matter what, practicing violence is not a solution. If you look at the situation you bring up of protecting your family, it is hard (at least for me) to argue against being violent in their protection. But Ghandi might question it and suggest that by practicing violence on that person putting your family in danger, you are simply lowering yourself to their level.
Of course that is easier said than done. It is also difficult for someone to think real carefully about the causes of violent behavior if they are the victim. If some guy hits me over the head with a 2x4 whilst I am walking down the street, I am going to be a lot more concerned with avoiding the next blow than immediately figuring out why he did it!
I think in terms of preventing future violence, examining the causes is of utmost importance. For a year I worked at a therapueudic wilderness camp for "at-risk" youth. Many of these teens were sent to our camp as an alternative to jail while countless others were there because they had serious anger management issues and were making the wrong choices in dealing with this at school and home. After 12 or 14 months of living in this environment (which for many felt more like punishment) this program graduated kids who were ready to re-enter society and function at school, with their families, and in normal lives without further incident.
This program mainly practiced "Reality Therapy." In this (the term was coined by Glasser) the reason for the violence or wrong behavior is not actually part of changing the behavior. Reality therapy looks at a goal - and what is the best way of achieving the goal. But I will say from experience with those kids, that it wasn't until they could talk through the reasons why they acted the way they did that they could begin to see their patterns and recognize when/how to make changes. The root causes (family issues, violent parents, drugs, negative peers in their real lives and rough lifestyles) were also eventually talked through. Again, the causes were never looked at as justification for the behaviors, but giving the behaviors a starting place was one of the biggest steps to recovery for these kids.
I think the same is true for most violent criminals. Like the first post says, outisde of self-defense (and this only to a degree) I don't think the reason behind the violence is ever justification for it - nor do I think it gives violence pardon. But in order to heal violent tendencies, I think it must be examined.
I think that assessing the causes and reasons behind any violence is extremely important. This is not to say that the examination of said causes should relinquish individuals from responsibility in their committing such actions. Yet, it is important to fully understand the causes and rationale behind the acts of violence in order to be able to fully eradicate why it happens. In terms of self defense, I think that this cause is evident enough in understanding. Someone acts in the interests of their family and protection of loved ones and does so in a violent way when these interests are threatened. I still think that there must be examination present because the pretense of protection of family has sometimes been used as a blanket cause for violence which, upon further review, has not been done for the expressed purposes as to what was said was done. I think that assessing and analyzing the causes for violence committed is extremely important and something that requires study and analysis.