Ever since Jon Walker and I pointed out the real and superficial similarities between Paul Ryan’s proposed RyanCare for future seniors and the Affordable Care Act (ACA) structure for non-seniors, numerous pundits have been trying to deny either the similarities or the differences.

For example, Ryan’s supporters are in denial that RyanCare requires a mandate, even though he admitted — just as the logic suggested — that he’d require future seniors to purchase a private health insurance plan from a government-overseen exchange. And ObamaCare supporters are in denial that their ACA insurance exchanges rely on pretty much the same faith in the ability of a mostly free private insurance market to sufficiently control health care costs and hence insurance premiums.

We’ve tried to categorize and distinguish Medicare, RomneyCare, ObamaCare and RyanCare — see, e.g., here, here, here, and here — some have tried to grapple with the distinctions, and others have tried to fuzz it all up to serve whatever agenda they had.

The latest effort to make something out of the similarities is from the Washington Post’s Steve Pearlstein, who provokes Paul Krugman into describing Pearlstein as a Very Serious Person, — i.e., someone who gets it wrong.

Krugman and DeLong (responding to Mankiw) address the question, “are non-seniors better off under the ACA/ObamaCare’s subsidized exchanges than they would be without the ACA?” If those are the only choices, their answer is “yes,” though I don’t think they’ve confronted the numerous “affordability” arguments Marcy Wheeler made when ACA was being debated. But let’s assume they’re correct. That still leaves the large question about how well the exchanges can control costs unanswered.

The Administration, Democrats and ACA supporters insisted the exchanges would work to control health care costs because competition within the insurance market would control prices while maintaining quality care and service. But I understand Paul Ryan to be making the same argument for RyanCare: his private insurance market exchanges will make health care affordable, he claims, because future seniors exercising choice when shopping in the insurance exchange markets will benefit from private market competition. Both rely on a mostly free market theory.

Either this claim and its faith in markets are plausible or they’re not. My concern is that when Paul Krugman (or DeLong citing him) talks about the merits of Medicare versus RyanCare, there’s a reminder that ever since Ken Arrow, economists have known the competitive market argument doesn’t work in this industry.

Even ignoring the already huge concentration in the insurance industry, and increasingly so in the hospital and other provider sectors, none of the elements required to make an industry amendable to effective competition and efficient market pricing exist. Therefore, RyanCare can’t achieve the cost savings Ryan claims. But government-sponsored systems like Medicare, because they can reduce administrative costs, and because they can exercise single-buyer market power that individuals in the exchanges will not have, can do better — and have done better, here and in Europe.

If that’s true, then it’s not enough for economists and other ACA supporters to argue the ACA should be better than not having insurance at all; they need to explain why Arrow’s analysis and real-world experience do not apply to the market-based claims for the ACA exchanges, just as they do to RyanCare. And if this is a fatal flaw for RyanCare, isn’t it also a fatal flaw for the exchange structure of ACA?