It's better to take a blow than to strike another. It's better to place yourself between a victim and a perpetrator, positioning yourself as a shield, and bear the brunt of the attack yourself, than it is to strike the perpetrator yourself.
Why?
Because nobody is beyond redemption. Nobody is beyond remorse. But by striking the perpetrator, you justify their unjust actions. Their reasons for striking are increased, in their mind. You may have stopped this attack, but not the next.