So I just got back into Destiny after not playing it since the month of launch, I remember there used to be a way to trade materials in groups of 10 for marks, now it seems to have flipped and you can sell marks for materials. As a strict PvE player I think adding the ability to sell materials for marks would be very helpful. It would let people who play PvE or PvP exclusively still have access to the other group's vendors. You still have the farming grind for finding materials but also a way to bring in marks from a play method that isn't yours. Sure, I suppose you could say it would take away from the "experience" of grinding but for people who don't play PvE or PvP (in my case) it makes it a challenge to do but still possible.