There is a banking adage that if it's growing like a weed, it's a good chance that it's a weed.

There is plenty of blame to go around for the U.S. housing bubble, but not much of it belongs to Fannie Mae and Freddie Mac. The two giant housing-finance institutions made many mistakes over the decades, some of them real whoppers, but causing house prices to soar and then crater during the past decade weren't among them.

The FHA's success provides strong evidence that government can and should play a role in the nation's mortgage finance system. It also demonstrates that although government intervention in the economy during the Great Recession was messy, things would have been a lot messier without it.

Defaulting on the nation's debt would be cataclysmic. The U.S. Treasury's Aaa rating is the one constant in the world's financial system. When times are bad anywhere on the planet, global investors flock to Treasury bonds because they know they will get their money back.

In a normal time, I don't think economic policy makes a large difference one way or another. But in times of crisis it makes all the difference in the world.

Potential home buyers have a two-step decision process. First, they determine whether they can afford to make a purchase - does their income safely cover their mortgage payment? Then they determine whether owning is a better financial choice than renting - are the costs of owning a home lower than the cost of renting it?

The most important point is, in a time of crisis, there is no way out but for the government to be bold and aggressive.