Netiquette or really any form of etiquette is not common sense. People in general do not know how to behave themselves in foreign cultures. As much as we might hate to admit it, cybercultures do abound and each have rules of behavior. They may not be posted, but members of the society know them. Many will be offended when these newbies, errm, newcomers enter the society and make blunder adter blunder.

So codify your rules (yeah, kinda like laws) so that newcomers will know what to expect. Also enforce them so that they retain meaning.