Now I believe I have found a way to add trading to Destiny that will make most people happy.
Step 1: It has to be anonymous, this will keep people from selling weapons on eBay.
Step 2: Equivalent Exchange, make it that to get an exotic you have to give an exotic. This will allows people who (if you read this you get a cookie)have too many of jellyhorns for example to get weapons they're missing and spread the love.
Step 3: Thorn, Bad JuJu, Invective, etc cannot be tradable. If you can "easily" get it than you have to get it.
You could even make it that trading is only available while Xur is around, removing the need for him to sell exotics.
Please tell me what you think of my idea, and add any improvements if you can think of any.
If you disagree please give a reason why not.