I played Diplomacy a few dozen times in college, and the idea of side deals or even carry-over irritation at a prior stab is foreign to me. We would have viewed an enforceable side deal as cheating, and we tried to convince others to ally with us due to game considerations.

Lying in-game simply isn't evil. Getting stabbed was part of the game. No one played meta-game vengeance tactics not because people didn't think of them, but because it seemed wrong to do so. Diplomacy's much more fun to play as a game, like any other, where you're trying to win the individual game.

And if you're in a situation where a stab is likely to lead to a much better in-game situation, you should do it. The discussions in this post are about a game I do not think I would like.

--JRM