If you were in a playground fist-fight, and your opponent picked up a baseball bat and started swinging it at you, would you proclaim “I’m sticking by my principles; I’m not going to use a baseball bat to defend myself, even though my opponent is attacking me with one”-—or would you pick up a bat?
This argument is as old as mankind and war itself. If attacked by an enemy, are you justified meeting that enemy with equal (or even superior) force?
It depends on whether my principles are not stooping to the tactics of the other side.
There is also a difference between a physical fight, and this.