What is it with Fathers and Physical Violence?

Rage.
Anger.
Aggression.

What is it which causes this type of destructive physical passion to be so close the surface in some men? Upbringing? Genetics? Nature? Nurture?
 After witnessing two recent altercations, I realize how much even the risk of physical violence tempers many interactions between men:

On the local toboggan hill:

There is one lane to the side of several runs specifically designated for walking to the top of the hill.
One father ignores this designation and returns to the top of the hill via a lane reserved for tobogganing. He has two sleighs and his small children in tow.
Another dad, already at the summit, yells down suggesting the father use the side of the hill for his ascent, thus not keeping anyone waiting.
Immediately the conversation escalates to an argument, personal insults, and a shoving match. It was on display not only for the dozen families present, but, most of all, for the young children of the two aggressors involved.

 In a cafeteria after skiing:

A discussion between a woman and an adolescent mutates into a shouting match. The woman's husband becomes involved. More yelling and swearing; all parties have to be restrained as a chalet full of families with young children, including my own, look on.

There are times I've been angry, very angry, although I don't know if I've ever experienced true rage to a degree which would cause me to physically challenge another person. There is certainly an element of fear in me, but more so what I would identify as sensibility. As much as I would not want my children to witness my being insulted, or my character diminished by another; nor would I wish for them to be by my side during a physical altercation. Whether I was the victor or not wouldn't change my perspective; I would want them to see me beaten anymore than I would wish for them to watch me beat on someone else. I can't imagine what a traumatic experience that would be.

With men, there is always an undercurrent of potential violence.
It manifests itself in incidences of road rage, where shaking fists often lead to invitations to pull to the side of the road. For what? Driving too slowly? Some imbecile being too aggressive?
This undercurrent also gives pause to those just looking for peace. In a movie theatre, I think twice before asking someone to whisper, please; or to darken the backlight on their phone. One can never be sure of the reaction of that man in front of you. Instead, I sit, I huff a little loudly. If the behavior continues, I may mention it to an usher – a poor sixteen-year-old who now has to deal with this dimwit. But, most likely, I'll let it go, or move myself out of the way.
Similarly when someone steps in front of me in line: if it's a woman, I'll risk an "excuse me", but if there is friction in the response, I'll give up. If a man wedges into line, I most likely won't mention it at all. It's not worth it.

Perhaps I'm a pushover.
Weak? Victim?
I don't know. I seem to be doing alright.
And when my kids ask me why those two men are fighting, I say: "Some kids never learn to use their words. And that's what happens."