While many other factors can be involved — rising incomes, population growth, construction costs — a scrutiny of the times and places where housing prices doubled, tripled or quadrupled within a decade shows restrictions on building have been the key.

Attractive and heady phrases like "open space," "smart growth" and the like have accompanied land-use restrictions that made the cost of land rise in many places to the point it greatly exceeded the cost of the homes built on the land.

In places that resisted this political rhetoric, home prices remained reasonable, despite rising incomes and population growth.

Construction costs were seldom a major factor, for there was relatively little construction in places with severe building restrictions and skyrocketing home prices.

In short, government has been the principal factor preventing the "affordable housing" that politicians talk about so much.

Politicians have also been a key factor behind pushing lenders to lend to borrowers with lower prospects of being able to repay their loans. The Community Reinvestment Act lets politicians pressure lenders to lend to people they might not lend to otherwise. The same politicians are quick to cry "exploitation" when the interest charged to high-risk borrowers reflects that risk.

The huge losses of subprime lenders, some of whom have gone bankrupt, demonstrate again the consequences of letting politicians try to micromanage the economy.

Yet with all the finger-pointing in the media and in government, seldom is a finger pointed at the politicians at local, state and national levels who played a key role setting up the conditions that led to financial disasters for individual homebuyers and those who loaned them money.

While financial markets are painfully adjusting and both lenders and borrowers are becoming less likely to take on so much risky "creative" financing, politicians show no sign of changing. Why should they, when they have largely escaped blame for the disasters their policies fostered?

Thomas Sowell is a nationally syndicated columnist.