Let's use a broader focus of thinking when talking about the "economy", stop looking only at the game itself.
Basics of an economy, circular flow of transactions in said economic environment through the exchange of goods, services, and money, mutually beneficial to all parties. You play the game's "jobs" to earn money to buy in-game items from R*. Trade here: game play for in-game rewards. Now comes DLC, another added "service" that R* is providing for you, in order to be beneficial to them, they must be compensated somehow. Now, since only a portion of players will be paying for this with real money, their reward for said "donation" if you will, is in-game cash to dispose of for added reward, increasing their equity in the game with extras that others chose not to pay for. Grinders still get their rewards by continuing to play and buy the same goods, and since everyone gets the DLC, there is still balance. What you guys need to remember to factor in, the in-game economy still includes you, the player, and R*, not just your character and their transactions.
Now, along comes glitchers, who obtained money through exploits that did not involve game play, or purchase of cash cards. They have now tipped the scales in their favor, devaluing the R* dollar by increasing the amount of money in circulation if you will. The perceived value of the in-game dollar is diminished in the sense that you no longer need to purchase their cash card, and hackers handing it out drop those numbers exponentially by taking out a number of those who would have bought them, they no longer need to. Basically, there's no reason for anyone to do the "jobs" anymore, money is spent frivolously. But R* is still providing services, updating programming and releasing DLCs, that they are not being compensated for. Numbers drop as players tired of being griefed or outgunned at every turn stop playing, further reducing R*'s potential compensation, in other words, economy broken.
Now, the only other plausible solution would be to stop the "Free DLC" notion, and just charge everyone at release. Of course, there will be endless bitching about "how dare they try to take more of our hard-earned money and turn a profit for their efforts", Catch 22. Fact of the matter is, people these days just love to bitch, and they want everything right now and they don't want to pay for it. But for those who don't believe an economy of sorts exists, you just aren't looking at it right.