I think that the Internet has taught us that when people feel anonymous, they will act like jerks. But I think road rage is worse than Internet rage, just because it can potentially be dangerous. When I'm driving, the only thing that matters to me is getting from point A to point B safely. If I'm a few minutes late to wherever I'm going, the world will not come to an end. I can't think of any place that I need to be exactly on time that is worth risking my life over.
Other people apparently feel differently.
There's this really difficult left turn I have to make when I leave work. The visibility isn't great, and of course everybody is speeding in both directions, which makes it harder. But on multiple occasions, I have made the turn with plenty of room, yet somebody has honked at me (and I mean really leaned on that horn) just because maybe they had to lift their foot off the accelerator for half a second. I'm not making a left turn as a personal insult to you, I swear. Honestly, when I see people trying to make what look like difficult left turns, I usually slow down to let them go.
I don't think people should be allowed to honk their horn out of anger. Horns should be used in order to prevent an accident, or possibly as an alert. That's it.
A friend of mine was recently telling me a story about how she was at a light and her car just died. She immediately turned on the blinkers, and most people recognized that she couldn't move the car and went around her. But there were one or two cars that just didn't get it, and kept honking and honking angrily. She said that one guy finally went around her, and gave her the finger and yelled curses at her.
I can't imagine what would make a person behave that way. Oddly, she told me she got out of the car after that, and subsequently multiple people stopped to ask her if they could help. Maybe after she was out of the car, she was less anonymous, so people felt more compelled to be nice?