If people are afk, then it's likely their pvp flag is off. So no, that's not a valid argument.
Also, are you saying that in a game called WARcraft, whose story is about WAR between Alliance and Horde, that neither of those factions should attack the other's capital cities?
You're either a casual, or you're just mad because you got rekt at some point.
If you have a problem with people raiding the city you're in, either move to a different city (shock!) or get together a defense group like a real man. Stop your whining.