itch.io

I played a LOT of MULE on Atari 800 with 4 human players, and collusion is a critical and fun element of the game.  Could it result in hurt feelings?  Perhaps, but it also allows a player with a monopoly on a resource to maximize their profit, try to maintain a majority resource position, etc.  I've been in many games where 2 players collude and later collude with others - it's not been my experience that it results in 2 players "dominating the game" against others.  If you have concerns about misuse, make it an option during game setup.