In "Writers often disavow the notion of a 'literary duty'" the author conveys a somewhat condescending attitude, as if they would always follow this and set aside anyone who said otherwise. This attitude says the author is looking down on them, and that the author believes that many authors do not meet their standards.
Another answer I would consider is "...writers ruined by their shrill commitments." However, there is no context or clear tone. The author could be mournful of the lost potential for all we know.
C. The speaker thinks that the colonists are being unfairly treated by the British government. Phillip Freneau is called the "Poet of the American Revolution". "American Liberty" was one of his literary pieces that is anti-British
