What is it about driving that turns some people into complete psychopaths?!

Today, I was driving down a 30mph road I have driven down at least 5000 times. I was in the left hand lane (it has 2 lanes). Through my wing mirror, I spotted a Silvery-Blue Vauxhall doing about 60mph cutting cars up for fun.
Being the sensible driver I am, I pulled over to let him pass. I half mounted the pavement so he had plenty of room.

Unfortunately, another car (A Gold Skoda) was in the right hand lane and seemed oblivious to the maniac approaching from behind. The Skoda was driving at the 30mph speed limit. As he got level with me, the Vauxhall tried to undertake the Skoda (he had millimeters to spare - literally). It looked like he clipped the Skoda's wing mirror but I can't be sure.

The two cars carried on, and I thought nothing more of it and continued down the road behind them. After about 400 yards, we hit a red light. As the traffic stopped, the guy in the Skoda got out of his car, ran to the Vauxhall and dragged the driver out. My vision was blocked by other cars from this point onwards, so I have no idea what happened. After around 30 seconds, the Skoda driver got back into his car and drove off (at the speed limit).

It is fair to say I was very shaken up by what I witnessed. I am a careful driver, and very patient (usually). I'm the annoying one who lets people out when we've been sat queuing for ten minutes at a junction! I am also very mindful of others when I drive. I was always taught it is not my driving I need to worry about, but the other idiots on the road. I had Sam in the back of my car. How would that Vauxhall driver have felt if I hadn't pulled over and he'd hit the back of my car and injured the baby? I am also 7 months pregnant so he could have had that on his conscience too, had I not been so observant.

Was cutting up other motorists for the sake of gaining 4 or 5 places in the queue really worth the risk? Not only the risk to himself after cutting up the wrong person, but the risk to other innocent 3rd parties. Seriously - If you're reading this, try to remember the next time you want to gain a few car places.... you MAY cut up the wrong person, or end up with more than punctuality weighing on your conscience.