Violence in and of itself is a negative thing, as it, almost universally tends to reduce the quality of life of at least one other person. In some circumstances though, violence can prove necessary to combat circumstances which could have a greater reduction in quality of life on an individual, or a reduction of quality of life in a greater number of individuals.
Although some people might claim that violence "should only be used as a last resort" often times in reality things like talking and negotiating can prove significantly less effective, and take a much longer period of time, thereby allowing these greater injustices to perpetuate to a greater extent, or for a greater amount of time in a way that a controlled usage of violence would not. In this manner, specific, and circumstantial uses of violence can be said to, if not increase overall human well-being, at the very least curb circumstances that would seek to DECREASE overall well-being (and therefore from a utilitarian perspective actually increase well-being, but I digress.)
Another thing to consider is that in some specific situations such as rough sex between consenting adults, or things like boxing or MMA, people can actually enjoy not only committing violence against others, but sometimes even having violence committed against themselves.
I think the short answer is that no action is truly good or bad in a vacuum, and the only way to measure "goodness" or "badness" is through consequences of those actions. Some actions such as acts of violence can be said to disproportionately effect the world in a negative way, and therefore it can be easy to say that those things are bad, however even among things that are disproportionately negative, it's far more useful to look at individual scenarios when evaluating things like morality and necessity than absolutes.