The ideas of economists and political philosophers, both when they are right and when they are wrong, are more powerful than is commonly understood. Indeed the world is ruled by little else. Practical men, who believe themselves to be quite exempt from any intellectual influences, are usually the slaves of some defunct economist. —The General Theory of Employment, Interest and Money

If by “practical men,” Keynes means men with power over others, then he is flattering himself and all other economists–including those who opposed his views.  Just as George Bush went out and found a someone who claimed he didn’t believe there was a housing bubble to be his Federal Reserve Chairmen, those in power choose apologists not influences.

The reason why economists become defunct is because they don’t provide justifications for people with power to do what they already want to do.

Is it only that simple?  No. Any person, powerful or not, can come under all sorts of influences for good or ill.  We can try to influence people, as long as we don’t get frustrated by unrealistic expectations.  But the fact is that “the ideas of economists and political philosophers, both when they are right and when they are wrong, are weaker than is commonly understood” and the economists who are less likely to offer justifications for power are both more likely to be right and less likely to rule the world.  And the powerful can as easily be influenced by superstitions like Ouija boards or astrology as by economists or philosophers.