If by 'scale,' you mean compute power, then it obviously depends on whether the processing power reaches some kind of saturation level. By analogy with graphics, we may well reach a point where centralized is 'good enough' to simulate decentralized, but may be preferable for some other reason. Or, once financial trading is 99%+ algorithmic, how much does it really matter who is running the algorithm?
The usual free market argument is that the actual information involved in a free market cannot be elicited in any centralized way, and I think this is what parent poster was referring to. The government can run a central mandatory trading house and, as long as it keeps itself from causing distortions for its own ends(*), this would broker most, if not all, of the information that a decentralized market would, with the concomitant benefits of centralization.
*: This is where it usually all falls down, of course.