Seth Godin has an interesting way of looking at the effect of anger here. We all know that a mood can spread, and we all encounter unbridled rage on a pretty much daily basis. We're often a little numb to it, and we really shouldn't. Anger, as with all emotions, has it's purpose.
Anger is one of the least productive emotions. It is paralytic, it prevents you from thinking or acting constructively, it's reactionary. The more that you infect others with your mood the bigger this problem becomes. You're the only one who can control your own anger; at the end of the day you're the only one responsible for it.