MICROFINANCE is an example of something that is sadly all too rare: an anti-poverty tool that usually at least breaks even. If you make small, uncollateralised business loans to groups of poor women, they almost always repay them on time. It has grown rapidly in many countries, not least Bangladesh and India. With nearly 30m clients each, these are now the world's biggest markets for microfinance. Yet the industry has come under attack for being too commercial.

In Bangladesh the government has capped the annual interest rate that microfinance institutions (MFIs) can charge at 27%. In India a new breed of for-profit microlenders has shaken up an otherwise NGO-dominated sector—and annoyed the authorities. In Andhra Pradesh (AP), the Indian state with the most microfinance borrowers and the base for the biggest for-profit MFIs, local politicians have bullied the business to a virtual halt. An interest-rate cap is mooted. These steps are ostensibly motivated by a desire to defend the poor from getting stuck in a debt. But they are wrong-headed.

Despite charging what may seem high interest rates, MFIs typically have wafer-thin margins because of the high costs of making and collecting payments on millions of tiny loans. Pressing them to reduce rates further would jeopardise their ability to attract private capital, inhibiting their growth. Slower growth would in turn hamper their ability to harness economies of scale in order to lower transaction costs and cut rates of their own accord, as many—including the biggest for-profit MFIs—have done in the past. Forcing down rates would also deter new entrants and reduce competition.

The rush to impose restrictions on MFIs also betrays a fundamental misunderstanding about how the poor use credit. Many politicians cite the existence of clients with loans from several MFIs at once to argue that the poor are over-indebted. This ignores the fact that most microcredit loans are tiny, so that several are needed to meet the needs of even a small business. Indeed, the poor often use microloans to pay off far more expensive loans from village moneylenders. This suggests that restricting people's access to microcredit by capping rates could have the perverse effect of driving more poor people into the arms of village loan-sharks, who still provide the bulk of rural credit in poor countries. (In rural AP, 82% of households have such informal loans, whereas only 11% have loans from MFIs.) That would be good news for these moneylenders, but is surely not the outcome that policymakers want.

Peruse prudent

Sensible regulation need not be at odds with a thriving microfinance industry. Peru, for example, is ranked by the Economist Intelligence Unit (our sister company) as having the best business environment for microfinance, in part because the regulator has successfully set and enforced rules on capital buffers, leading to a more stable environment for the industry. India, in contrast, is yet to decide whether rules governing microfinance are to be set at the national level or by individual states.

An association of Indian MFIs is trying to set up a credit bureau which would allow them to track clients' overall indebtedness and credit histories, thus guarding them against lending a person more than she is able to handle. This would be helped enormously if the government speeded up its efforts to give all Indians a universal identification number. The Indian government should also allow MFIs to take deposits, which they are currently prevented from doing: this would make them less dependent on capital markets for funding. All rather complicated things, unlikely to stir up populism. And all a lot more useful for the poor than an interest-rate cap.