Law of the Game postulated that gold sellers would make an effective way to launder money for criminal organizations. Now, I can't say that I find his idea to actually have to pay real tax in-game money (which, at least in WoW's case, isn't even really yours, as Blizzard has repeatedly stated that all in game items and assets belong to them) but I can understand that, if Symantec is right and real life criminals are using our MMO hobby as a means to not only make money but to clean up money made from other, illicit activities, then eventually something will have to be done to make it less attractive to them. At present, gold selling or RMT (real money trading) is a incredibly safe business for people to commit crimes with (as, for an example, stealing your password in order to convert all of your character's gear to gold that can be sold to others) because it's new territory.
The new danger would be that not only is there money to be made in the trading of on-line gold and items, but there's even more money to be made in using that trade to conceal yet more money made through already established vices and crimes. Which, to be honest, kind of messes with my head: the idea that someone pretending to be a stealthy rogue or bloodthirsty brute of a warrior could in fact be helping honest to murgatroyd killers, thieves and pushers to conceal how they made their money by buying pretend gold with real money.