Greg Mankiw is an economist at Harvard and the author of economics textbooks. He recently wrote and excellent piece in the New York TImes, When the Scientist Is Also a Philosopher. I really appreciated this excerpt.
...We economists often have only a basic understanding of how most policies work. The economy is complex, and economic science is still a primitive body of knowledge. Because unintended consequences are the norm, what seems like a utility-maximizing policy can often backfire.
So, what is the alternative? At the very least, a large dose of humility is in order. When evaluating policies, our elected leaders are wise to seek advice from economists. But if an economist is always confident in his judgments, or if he demonizes those who reach opposite conclusions, you know that he is not to be trusted.
In some ways, economics is like medicine two centuries ago. If you were ill at the beginning of the 19th century, a physician was your best bet, but his knowledge was so rudimentary that his remedies could easily make things worse rather than better. And so it is with economics today. That is why we economists should be sure to apply the principle “first, do no harm.”
This principle suggests that when people have voluntarily agreed upon an economic arrangement to their mutual benefit, that arrangement should be respected. (The main exception is when there are adverse effects on third parties — what economists call “negative externalities.”) As a result, when a policy is complex, hard to evaluate and disruptive of private transactions, there is good reason to be skeptical of it. ...
This is the point I've tried make on so many occasions. My opposition to many policies is not so much grounded in ideological fidelity as it is in epistemological humility. I have severe reservations about the proponents' ability to accurately understand secondary and tertiary consequences that can result from massive interventions.