[pessimizer]

The kind of "nice" in board games that is bad is when a player is willing to lose in order for another player to win. When you play a game, everyone has to play to win for the rules to make sense (I'd argue almost definitionally for a competitive game.) Playing a board game with someone who is not playing to win is like playing tag with somebody who refuses to run away and won't chase you. You should be working on a puzzle together or writing a song instead. Maybe make up new rules every turn and pantomime playing the game, that's fun.

The kind of "nice" that is good in multiplayer board games is strategic. Being "nice" isn't necessarily being nice. If a subset of players collaborate, they eliminate the other players from the game. It's one of the ways most multiplayer games naturally handicap based on the reputations of good players - other players assume that they will get the short end of any deal with a good player, so refuse to collaborate with them.