The reason auction houses and trading works in traditional mmos is because there is actually a very very wide nearly infinite amount of different pieces of gear. In Destiny literally everyone is looking for the four pieces of raid gear. A trading system in Destiny would make it so anyone with duplicates of items could get basically anything they want for nothing. I have two gjallarhorns, two icebreakers, and two hawkmoons, just by trading my duplicate items I could likely get the three raid pieces I want without even having to step into the raid. Is this fair? Games should encourage players to actually play the content, trading just gives people more avenues to avoid actually playing the game.