tsuwm, I wonder if your last paragraph above could cause someone to mis-read Rule 3 as saying, in effect, "What is, is how it will be, and if you don't like it, tough." To clarify, I repeat that as you already noted, t the gloss on the rule indicates a different meaning: "Get a sense of how the people who are already there act. Then go ahead and participate."
And of course this is tempered by the other rules -- I'd think particular emphasis would fall on the rules that come first. Rules 1 and 2 (and extracts from the gloss):
"Rule 1: Remember the human Do unto others as you'd have others do unto you. Imagine how you'd feel if you were in the other person's shoes. Stand up for yourself, but try not to hurt people's feelings.
Remember the Prime Directive of Netiquette: Those are real people out there. Would you say it to the person's face? If the answer is no, rewrite and reread.
Rule 2: Adhere to the same standards of behavior online that you follow in real life Perhaps because people sometimes forget that there's a human being on the other side of the computer, some people think that a lower standard of ethics or personal behavior is acceptable in cyberspace. The confusion may be understandable, but these people are mistaken. Standards of behavior may be different in some areas of cyberspace, but they are not lower than in real life."