Bungie has already covered this and there will be NO trading in D2. If you want to level up you have to do the grind. If you want a item then you have to obtain it yourself especially if you need to do a specific activity. The grind to obtain anything is part of the game and incentive to do a certain activity. You are not getting around that fact by getting someone to give you everything. Also any trading system would be abused by certain parties as they would charge real money for items.