ive killed people to win a game of diplomacy. The court didnt think the "the rules say i can do anything to I want" defense was very good.
zeriously [i noticed this was misspelled, but decided it was better that way] though, metagaming DOES break the rules. You can make any deals or do anything you want to win the game. Notice that 'the' is singular, as in deals cant be outside the scope of that game.
Now with that said, i have no problems with spouses or friends or whomever playing as a team. Thats totally acceptable because it is effectively no different from making an alliance with someone every game. Since each game is distinct from the next, it is perfectly fine to ally with someone at the begining of each game. Metagaming is just a bad strategy because country assignments are random. Look at it this way.Germany and austria almost never attack each other early on and no one would say that germany and austria start as allies. So if a pair of metagamers always started as germany and austria, you would hardly notice. However, the chances of starting as adjacent powers every time is slim and even then, it doesnt eliminate the need to make deals with other powers. All the deals are made within the scope of the particular game. In the case of the endlessly allied metagamers, they are only breaking rules in theory, not in practice. Ultimately there are other players on the board and, just like any other strong alliance, if other players suspect it, they will team up against them in order to maximize their chances of winning.