> If people are nice to each other in a way that makes them hard for you to beat, surely it is you who are playing the worse strategy by not doing the same?

If the arguments that underly the strategy decisions taken during the game purely happen during the game, that's perfectly fine. The issue arises when you absolutely cannot do anything to influence those. Rules of games are designed not designed to account for external behaviours that might favour

Eg: If Alice, Bobo and Charlie are playing a game of Risk and Alice is in love with Bob in real life and won't do anything in the game to hurt him. What can Charlie really do ? The rules of Risk have been designed to give each player with equal skill roughly 33% chance of winning - as they should. But in this case, Bob is almost sure to win and Charlie has very little things he can do to change that. How is that fun for Charlie ?