That does not mean that anything goes. Goldwater restating Cicero probably overstated the case. It made for fine oratory to say "Extremism in the defense of liberty is no vice" but the job of a Statesman, or Officer in combat, is to determine what, given the goals, is sufficient and to draw the line between necessity and extremism. It means that something goes and the forces of freedom must decide what is needed to achieve their goal.
At Harfleur Henry V according to the Bard threatened,
Once he had the governor's surrender Henry commanded "show mercy to them all." Napoleon was no champion of Liberty, but he probably was justified in dispersing the crowd and preventing further bloodshed at that time.
If not, why, in a moment look to see
The blind and bloody soldier with foul hand
Defile the locks of your shrill-shrieking daughters;
Your fathers taken by the silver beards,
And their most reverend heads dash'd to the walls,
Your naked infants spitted upon pikes,
Whiles the mad mothers with their howls confused
Do break the clouds, as did the wives of Jewry
At Herod's bloody-hunting slaughtermen.