That's a complicated question, one that can't really be answered by a simple poll.
How do you define nature? It isn't a simple blueprint or a written code that determines if you are violent or not, as the conditions which constitute violence vary. Personal experience, environmental factors and socioeconomic conditions play factor.
For some, the warrant for violence exists for something that is older than man itself: Survival. Resources like food, water and recreation are very important to the stability of the human ego and its long term survival and comfort in the world. When one doesn't have those things and goes without, they can become desperate and are willing to attack and or kill others to make betterment for their lives. Whether it is in the fictional realms of post apocalyptic society, crime drama or the unfortunate conditions that make up our reaity, desperation and chaos create a state of vulnerability for humans and thus force them to battle one another over resources.
Another constitution for violence is the vacuum of power. Just as the worst off of society may be more inclined to resort to desperation, those with power tend to be more inclined to resort to violence to maintain their power and maintain the state of privilege they own, whether it be someone of great wealth resorting to physical threats against competition or a state going to war with another, either for resources or ideals of honor or glory.
But things are not always so simple: For reasons of a more complicated nature, people may be inclined to turn to violence for pleasure due to psychological conditions or embracing certain ideologies. One can assume that these people were born these ways, but as humans tend to be products of their environment, this is a vast oversimplification. Can one raised with the pretense of "Do onto yourself, what others do to you" and "Glory to Leader/God/Ideal" be inclined to the same conditions? Just as so, what creates the conditions to turn a human born into a blank state into a serial killer that revels in violence? This is a struggle for psychologists, sociologists and ultimately the close examination of the society we live in that creates the conditions for tendencies to come to fruition.
Not all violence is motivated by ideology, or lack of a need however, though they may perhaps be contributing factors to the following. In a more grey light, acts of violence against oppressive individuals and institutions, such as oppressive governments who oppress their populations, and malicious individuals and groups who would otherwise seek to harm you or your loved ones through force and violence of their own, may be necessary in situations where they cannot be dealt with otherwise.
In conclusion, are humans naturally violent? If it is a simple matter of if it is a viable option for humans to deal with situations using violence in cases of desperation and survival, then yes. However, the conditions we live in, such as access to resources and socioeconomic factors tend to push the need for humans to be more violent. These conditions which are, in terms of todays society, is unnatural to the condition of man. Violence can be used to protect yourself and others, to create what you see is a better world, defend power, or just to hurt others in a state of twisted bliss. It is evident, however, that violence as a whole tends to put a huge amount of distress on humans, both individually and collectively and is seen as harmful to a large degree. We should not be asking, "Is violence natural?" And instead, try to improve ourselves, eachother, and help to make a better world where conditions can be better for all, reducing the need for humans to be violent, and in doing so, creating a happier existence for all.