To be honest, I'm not sure the bikers' response was THAT unreasonable. Obviously now that I know the driver was just a guy trying to protect his family, I can understand his actions. But in the heat of the moment, the only thing most of these bikers saw was some crazy SUV running people over. I'd be PISSED if I saw someone hit my friend and drive away. Not saying I'd chase him down, pull him out of his car, and beat him up in front of his family.
After all, this was New York, that greatest city in the world