Frances Coppola's account of Lloyds' high-powered incentives to staff for mis-selling products raises two general issues. To see them, read her description alongside allegations that RBS forced some of its business borrowers to close in order to acquire cheap assets.

Both these episodes are evidence against the Friedmanite hypothesis that businesses act in the public interest by maximizing profits. Better still, they show two of the circumstances in which Friedman's theory goes wrong.

One is if firms have significant market power. Had RBS's customers had alternative sources of finance, they could simply have borrowed from others, thus escaping RBS's clutches.

Another is when there's asymmetric information; Lloyds would not have been able to mis-sell products if customers had been well-informed about their shortcomings.

It would be a stretch - the commission of the journalist's fallacy! - to claim that these examples show that Friedman was entirely wrong. Instead, they suggest that he is right only in circumstances where corporate power is constrained.

The second issue is that these latest examples of banks' malpractice occurred whilst they were in public ownership. Which raises a paradox. When banks were privately owned, they mis-served the public interest by making huge losses and triggering a financial crisis, but when they were nationalized, they mis-served the public by being too zealous in the pursuit of profit. This is the exact opposite of the conventional wisdom, which says that privately-owned businesses maximize profits, whilst nationalized ones often have other objectives.

There's a simple reason for half this paradox. The banks were nationalized with the intention of restoring them to profitability quickly; in this sense, RBS and Lloyds were doing just what the government wanted. The government's attitude to banks has been that of a leveraged buy-out fund, using debt to invest in distressed firms with the intention of returning them to the stock market at a profit.

Nevetheless, this poses a more general question: what function does ownership serve? The financial crisis showed us that private ownership failed to prevent inept CEOs from making big losses. But Lloyds and RBS's behaviour shows that public ownership is not sufficient to make businesses act in the public interest either. This suggests that - for some businesses at least, neither form of ownership is, in itself, adequate.

However, the question of which forms of ownership are best for which businesses seems to be one which is, to a large extent, off the political agenda - which is yet another example of how mainstream political debate is narrower than it should be.