This country has a long, and revered history of anonymous political commentary, beginning with Thomas Paine, the author of the widely read pamphlet, Common Sense (1776), which advocated for America’s independence from Great Britain, and The American Crisis (1776–1783), a pro-revolutionary pamphlet series.
Our founding fathers also utilized the ability to anonymously make political commentary in the creation of our country. The greatest example of this is The Federalist Papers.
The Federalist Papers are comprised of 85 articles advocating the ratification of the U.S. Constitution, and were originally published between October 1787 and August 1788. They were written by Alexander Hamilton, James Madison, and John Jay, using the pseudonym "Publius," in order to preserve anonymity and to ensure that the ideas were considered on their own merit, separate from the authors of the ideas. These papers are still today a primary source for interpretation of the Constitution, being that they outline both the philosophy and the motivation for the system of government being proposed.
Another excellent, and more recent example of anonymity in political commentary, is a book written by a Bush administration official/whistleblower, Imperial Hubris: Why the West is Losing the War on Terror. The author is now known as Michael Scheuer, a CIA veteran with 22 years service, who ran the Counterterrorist Center's bin Laden station from 1996 to 1999.
There are many possible reasons for wishing to remain anonymous when publishing political commentary. One may wish to be anonymous in order to avoid family problems, or to avoid issues with their employer, or to avoid retribution by political figures, or even to avoid being found by an abusive ex-spouse. All are legitimate reasons, and it is a choice that is available to each of us who writes or speaks out.