This is a really interesting question. My first reaction is that violence is never the answer, but then that's not really the whole truth is it. Furthermore, as a parent too (though I don't have boys) I have experienced my kids being 'bullied' at times and wanted them to 'stand up' for themselves more than they have.My husband and I have talked to our kids about being confident and not letting people 'push them' around.
But ultimately, in the playground or classroom, you are not there and words are just that - words. Some kids are persistent and don't let up, and your child may become the target. We've encouraged first facing off with the individual and working it out - non-violently, then ignoring the behaviors and finally speaking out (to the child, to peers about the situation, to teachers) especially if there are verbal or physical assaults that are really abusive or disturbing.
Remaining silent is not an option. Our children are relatively stoic, so we need to encourage this. For lots of kids, fear of being teased for 'telling' keeps them silent for too long.
As far as when violence is acceptable, that's up to you. Each parent must decide what to teach.In my opinion, most violence can truly be avoided, even by kids. Confidence around friends can telegraph a child's sense of self and perhaps keep the bullies at bay.
Self-defense classes - like karate or other martial arts - are examples of sports that might help certain kids develop increased confidence and also learn some body control and develop strength. Other sports can help increase confidence and overall strength too. Other hobbies, for the right children, can provide additional areas of focus and confidence - like creative arts and music.
Just teach him never throw the first punch. Let him know it is never right to step up to someone but if someone steps up to him it's alright to hit them.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.