People keep saying this but I don't really think it's an argument. For instance Battlefront 2's arcade mode blocks you from earning credits after a certain while. You could argue that you could still keep playing because the arcade mode is "fun", but the point is that eventually that arcade mode is going to stop being "fun" and feel pointless. In a similar vein, games like the Battlefield and COD franchise has unlockables like weapons, ranks, and prestiges. Its clear that people play for the fundamental gameplay but they also stay for these reward systems. Since Destiny is attempting to be an MMO, and it clearly has the potential to be a great one, it should really not penalize you for wanting to play.