Violence, a term filled with ethical and political meaning, is a central concept for defining social relationships between people. It is clear in some, perhaps most, cases that violence is unfair; but, in some instances, someone's eyes seem more debatable: can violence ever be justified?
Self defense
The most logical reason for violence is that it is done in retaliation for other violence. It will seem justified to try to react to physical aggression if a person punches you in the face and seems to be willing to keep doing so.
It is important to remember that violence, including psychological violence and verbal violence, can come in various forms. The argument in favor of violence as self-defense, in its mildest form, argues that an equally violent response to violence of some kind can be justified. Thus, for example, you may be legitimate to react with a punch to a punch; but you are not justified in responding to mobbing (a type of psychological, verbal and systemic violence) with a punch (a form of physical violence).
In a more daring version of the rationale for violence in the name of self-defense, violence of any sort can be justified in reaction to violence of any other kind, given that the use of violence in self-defense is quite rational. Therefore, it may also be necessary to use physical violence to react to mobbing, given the violence does not surpass what appears to be a reasonable payoff, adequate to ensure self-defense.
In the name of self-defense, an even more audacious version of the rationale of violence has it that the mere chance that violence will be committed against you in the future gives you ample excuse to practice violence against the alleged attacker. While this scenario happens repeatedly in daily life, it is definitely the more complicated one to justify: how do you know, after all, that an offense will follow?
War
For the ties between states, too, what we have just addressed at the level of individuals can be kept. If physical, psychological, or verbal abuse is at stake, a state can be justified in reacting aggressively to a violent assault. Likewise, according to others, it might be justifiable to react to some legal or institutional violence with physical violence. Suppose, for example, that State S1 imposes an embargo on another State S2 such that immense inflation, shortages of primary commodities, and consequent civil depression would be endured by citizens of the latter. While one might argue that S1 did not impart physical violence against S2, S2 may have some reasons for a physical response to S2.
In the tradition of Western thought, and beyond, matters concerning the justification of war have been addressed at length. Although some have repeatedly advocated a pacifist viewpoint, another author emphasized that it is inevitable to wage wars against some criminals on certain occasions.
Idealistic vs. Realistic Ethics
In pointing out what might be labeled as idealistic and rational approaches to ethics, the debate on the justification of violence is a perfect example. The idealist would insist that violence can never be justified, no matter what: humans should aim for ideal conduct in which violence never figures, whether or not that action is achievable. Authors such as Machiavelli, on the other hand, answered that while idealistic ethics would work perfectly well in principle, such an ethics can not be practiced in practice; considering again our case in point, people are violent in practice, so attempting to have a non-violent action is a policy that is intended to fail.
Wonderful and educative, we should also remember, violence should be our very last option, other means should be tried and carried out before falling back to violence