"* I said earlier that insurers can’t charge premiums that are less than the expected cost of your care unless they can make it up on the healthy customers, and they can’t in the individual market. But if all insurers are prohibited from doing medical underwriting (pricing based on healthiness), then they will all have to overcharge the healthy customers, and the system could work. This is still a tricky issue – and single-payer (like Medicare) would be much simpler – but it can be made to work even in a competitive market."

We don't know that it can work, because we haven't seen it work. There's no evidence to back up the claim that it "can be made to work".

Although this is why I try to explain to people that insurance is a financial instrument, not a health care delivery tool. In this scenario, the financing, which is failing right now, is bolstered by growing the market, overcharging some based on care needs, undercharging others, and using taxpayer funds to close the gaps. It really actually shifts more of the burden to the middle class, not to the private for-profit insurers.