From the original manual
"Even among enemies as bitter as the Horde and the Alliance, there is honor. If you flaunt this honor and engage in objectionable PvP play, such as killing new players vastly inferior to you in level, or killing essential non-combat NPCs such as flight masters or quest givers, you will earn dishonor. If you accumulate enough dishonor through your criminal actions, you will be branded an outlaw. As a consequence, you’ll suffer experience penalties, lose access to your own faction cities, and become so hated even by your own kind that every faction NPC will attack you on sight."
Blizzard scrapped this system when beta ended as they didn't spend enough time on it and it was too punishing. I think it would be fun to make the reputation system in WoW more fluid. Maybe even allow races to cross over to the other faction if they grind enough dishonorable kills or kill their own faction.