A valid rationalization but never an excuse. At some point the buck has to stop being passed around. Standing up to all instances of violence is the only way to stop the endless cycles.

Clarification: I never justified what bullies do, just giving an explanation. I should have made more explicit that punishing alone accomplishes nothing if the source of the problem isn't addressed: they just go to the next easier victim.

that is not a valid reason for others to suffer their cruelty and not apply effective self-defense