Email is communication. It requires the sender to communicate an in a way that the receiver can understand. It requires the receiver to participate in decoding the message, and to ask for clarifications if things are misunderstood. It requires give and take. When give and take does not occur, when assumptions get made, when pressures are brought to bear, when ego is allowed to go unchecked, you get miscommunication and escalating tensions. On a mailing list, it’s only worse. A dozen or so well-meaning hotheads misunderstanding each other soon results in the harshest of flamewars.