It *is* based on "metagame factors". 4E asks that you recognize that when you and your friends sit around a table and play a game, you are in fact sitting around a table and playing a game.
The "credible threat" rule is there as a way to formalize the general social contract of a roleplaying group: "we're all here to have fun, so let's play the game and not abuse rules loopholes."
As this thread has demonstrated, this bag of bunnies idea has caused a tremendous amount of people to roll their eyes in exasperation (that's putting it mildly). Try it at a table of reasonable gamers, and you'll get the same reaction.
So huzzah to 4E for going so far as to put "play nice with others and don't be a dork" in the rulebook.