Originally Posted by Zeful
The "Gentleman's agreement" is one of the worst things to happen to roleplaying games, it binds the DM's hands in the sense of "fair play" without doing the same for the players, making the game require an excellent DM to even adjucate the game, and essentially making the effort in becoming a great DM not worth it. It's pretty much the archetypal example of the arguments that raised the Oberoni Fallacy. "It's not broken, the Gentleman's Agreement/Rule 0 fixes it."
I'm entirely failing to understand the line of reasoning here. To begin with, all the definitions of gentleman's agreement in the context of RPGs include the players agreeing not to break the game. That is, both sides (DM and players) agree to be gentlemen!
In a horribly ironic twist, the specific tactic and situation you appear to be endorsing here (i.e., the system expects a new DM to allow an item or spell or feat, later discover it to be broken, and then remove it, thus ensuring that the game is not imbalanced) is in fact Oberoni in nature. And would be solved equally well by an actual gentleman's agreement.
A well-designed system, ideally, needs no after-the-fact fixing; DM fiat and mutual agreements not to break the game are both designed to cope specifically with flaws in the design that show up later, and should not be considered during the actual design phase (or when discussing problems that need fixing).