Somehow, someway, the mod developers need to come up with a system that (a) allows one item to be traded for another item based upon this idea of "equivalent exchange", but (b) doesn't allow the system to be abused. But how would that be possible? My plan, before I realized just how fast you can make Red Matter in the ProjectE mod (really, really fast), was to make an assembly line of MFR Auto-Spawner sending Villagers into a Tinkers Construct Smeltery for infinite emerald supply. How can any "equivalent exchange" ever hope to work when you can always find some way to create infinite materials?