Road Rage

I witnessed my first road rage incident yesterday and I am still haunted by the sight of a large man in his 30s trying to drag a man in his late 60s (or older) through a car window whilst punching him in the face! All because the older man dared to beep his horn at the car the younger man was a passenger in that had stopped in traffic and blocked the exit.
This was bad enough, but what perhaps was worse was that we were in rush hour traffic with cars and vans backing up on both sides of the road and no-one, NO-ONE, got out to help the old man. I eventually leant on my horn to at least draw some attention to what was going on and then a few followed suit until we were all so loud and insistent that the younger man got back in as the traffic moved and the car drove away. As the older guy drove away - obviously shaken - he nearly caused an accident as the lights had changed and cars were just driving round him.
Now, by this time I too am slightly shaken and extremely indignant. As I pull into the supermarket car park I call the police to report the assault - having taken the number plate of the car - and they can't/won't so anything unless the older guy actually reports the assault himself.
How can it be that anyone thinks it's Ok to act this way? and how can it be that the system is set up to let someone get away with such bullying and frankly criminal behaviour. I despair!