What exactly is the difference between "the complainer is always wrong" and "do unto others as you would have them do unto you"?
- Not sure what the basis for that comparison is, unless you're taking "the complainer is always wrong" as a positive. It's not. Even where that's the intended message, it's seen (by modern eyes, anyway) as either conformist glurge ("everyone should get along") or lazy writing ("Bob brings up a legit point. But he's still wrong. Because reasons.") "Do unto others" is often a positive message, and even when it's wrongheaded in its implementation, you can see the intended message.
- Still, what's wrong with just getting along with other people? And what measure is a complaint?
- Ask that to the people who refuse to get along with the complainer. The point of this trope is not that the complainer is an asshole who can't get along with others, it's that the group is actively guilt-tripping the complainer into accepting the group's opinion without compromise or accommodation.
- "The complainer is always wrong" means that they think that a bad thing is wrong, and his friends are assholes until the first guy does it anyway. "Do unto others" means that they thing a bad thing would suck for them, and thus don't do it. If their friends made them continue or start doing it to "fit in", it'd have both.