After repeated Volscian provocations, the Romans eventually invaded and despoiled Volscian territory: Livy describes the differences between what the Romans and Volscians did in this way,
The Roman devastation of the land was consequently quite unlie the sporadic forays made by the Volscians who, like bandits, relied on disagreements between their enemies, but feared their courage, and acted in nervous haste; it was carried out by a regular army in lawful retaliation and did more damage because it was not pressed for time. The Volscians had in fact limited their incursions to frontier regions, for fear that any minute an army might march out from Rome. The Romans on the other hand had a further reason for lingering in enemy territory; they hoped to provoke the Volscians to give battle. And so they burnt down all the farm buildings everywhere and even some of the villages, left not a single fruit tree nor an ear of corn standing to give hope of a harvest, took off as booty all the men and cattle outside the town walls, and then brought both armies back to Rome. (VI 31)
The Romans were obviously, if we believe Livy's account, more vicious than their Volscian enemies: the impact of a Roman raid was deeper than the impact of a Volscian incursion. The real issue is why. Livy offers us an answer- which is that the Volscians feared a Roman army more than the Romans feared a Volscian. He bases this argument upon the fact that Rome was a civic society whereas the Volscians were an agrarian one. This suggestion deserves our attention- however even if we accept Livy's social division I think we can go further than the Roman historian in attributing reasons behind his observed distinction.
Two things instantly come to mind. The first is that the purpose of the Volscian invasion was not neccessarily the same as the purpose of the Roman invasion. Livy may, reading his sources, be confusing Volscian invasions with Volscian cattle raids: raids across the border which sought plunder and had no political purpose. It seems to me pretty obvious that this would be the basis for much interraction between Roman and barbarian across whichever frontier that they lived upon. On the other hand, the action that Livy describes is the civic response to those raids- a punitive expedition which is designed to punish and not merely to plunder. The first kind of invasion is a quick attack for the purpose of gathering booty- as soon as you have your goods, your interest is to get back to enjoy the proceeds of your raid. The second expedition is designed to punish the raiders- and so you go as deep as you can and punish as much as you can. The second thing, tied to the first, is that the Romans may have been much more coordinated than the Volscians- they had an army as opposed to a raiding band and so their damage could have been organised, instead of a matter of whim. With a more methodical approach, more devastation could be achieved: organised violence can be more focussed and hence more damaging than disorganised violence.
The basis for Livy's point is his division between civic and barbarian societies: he may not at this point in Roman history be right- indeed I would suggest that Livy is still writing without evidence particularly without the Volscian side of the story. More often than not, I would suggest, he bases these ideas upon his own knowledge, gathered through conversations with Augustan commanders about their relations with Germans on the frontier. Be wary though of the dichotomies that Livy invokes: it may be that really what we are looking at is not so much the dichotomy of ability to commit violence between these two types of society as a dichotomy of intention. As I have suggested if you intend to gather wealth, then devastation is an incidental byproduct, if you intend to punish then devastation is your first principle and hence you are going to devastate more. There may be organisational differences as well- but this point explains the cowardice of the Volscians better than any story of Roman bravery: Volscians retreated before an army because their purpose was to get plunder, not to fight, the Romans sought to fight because they wished to destroy the raiding capacity of the Volscians.
In this sense, I think, if we unpick Livy's narrative, we can both see his assumptions (the virtues of civic society) and also the reasons that lie behind some of what he observed (of the Volscian-Germans) : it may not always be that societies differ in courage or moral intention, but it may be that their activities have different consequences because they have different purposes. The Volscians sought to gather goods, the Romans sought to punish them for gathering goods and that explains the difference in their actions when on enemy territory and also the different impact of their raiding.