Perhaps, but that will cost them money, and at the least get their attention. And if they have to pay legal fees AND fines, they'll do something to reign in their kids, in most cases.
Self-defense is always acceptable behavior. And when taken off school property there's less likelihood of involving teachers and administrators. And mostly, getting the primary bully (there's always a primary, the others tend to follow his/her lead) away from his pack can really defuse the situation. So many of these people are weak and helpless on their own. Showing your strength in a place where his followers can't see his cowardice can make a huge difference.A last resort, I think, seeing how you do the same as the perpetrators, but saying it is ok in a good cause..There is too much of that already.
And sometimes a knee to the groin, or an "accidental" elbow to the nose as you make a sudden turn, is enough to let them know you can't be bullied with impunity. That's a hard way to go, though. Most of the people the bullies like to pick on are the quiet, non-confrontational ones.
The WHY is basic in-group/out-group dynamics. The way they use the net is based on the perceived anonymity it provides. Exposing them and their actions for what they are has been helpful there, at least.Maybe the talking about these things in homes and at school AND online can turn the tide. Bottom line, the question I think is WHY they do it, and attack there. I do not mean the individual reasons, but the way they use the net.