I was struck by this quotation from Howard Zinn in The Art and Craft of Writing Historical Fiction, by James Alexander Thom:
Historical fiction and nonfiction are both abstractions from a complex world of infinite fact. Both can tell the truth; both can lie. The "lies" (that is, distortions, omissions, exaggerations) in historical fiction may have two advantages over the "lies" (that is, omissions, exaggerations, distortions) in nonfiction.
Some good commentary on the difficulties of both historical fiction and history writing.