Critics of Israel urge Israel to exercise "restraint." To that I'd make a couple of observations:
i) In just war theory, there's the principle of proportionality. However, that doesn't mean you should use the same amount of force as the enemy. Rather, the means should be proportionate to the goal. Don't use force far in excess of what's needed to secure the strategic objective.
But war isn't a sport, as if you should give the enemy a fair chance of beating you.
Imagine if two men, wielding baseball bats, break into your own at night and threaten your family. Are you supposed to defend yourself with a baseball bat, or reach for a gun (assuming you have a gun)? You're hardly obligated to be "fair" to the assailants by using the same weaponry.
ii) "Restraint" assumes your enemy is prepared to give in. If, on the other hand, you have a fanatical, implacable foe who will fight to the last drop of blood, then the enemy doesn't allow you to exercise restraint. He's forcing your hand.