We are only allowed to choose one because it cuases players to choose a specific playstyle and adapt to the challenges the game presents. If we could use as many as we wanted then it would be pretty hard for bungie to make content that is challenging to us because we would be able to used something that is equipped for every situation simutaneously. Their decision to only allow us one causes a flow to the encounters in the game and more decison making on our end. Destiny wouldn't be very fun if we could easily blow through every situation due to too many weapons that suit every situation we would ever face. So I would argue they are promoting fun actually.