I find attractive your theory that history should be taught from an unpolemical perspective (inasmuch as possible) because we need to equip children with analytical and critical thinking skills, rather than imposing values upon them (i.e. capitalism is good and inevitable, democracy is without flaws, etc.). Values are which are 'learned' and 'understood' are much more powerful, durable, and influential than those which are imposed upon us. It is essential that we teach our youth the ability to understand both sides of an argument, rather than pushing them to become ideologues who lack the ability and skills to analyze the effects and implications of their beliefs. It is better to teach children why communism/Nazism/fascism is attractive, and then have them internalize that perspective, which will allow them to understand why Germany voted in the Nazis, or why Lenin became a Marxist; because it will then allow students to learn the lesson that ideologies which may be attractive in theory may turn out to be dangerous in practice, or that good ideas which gain popular traction can become corrupted and perverted by leaders who succumb to the temptations of power. We often try to "otherize" the Nazis and Communists; but instead we should seek to understand that they were human and that their decisions were driven by human instincts; rather than dehumanize them, we should try to understand what aspects of human nature led to their misguided decisions and results, which can only be done by internalizing their perspectives, so that we can learn and comprehend the lessons to be learned from the history of the 20th century. Students who lack the skills to internalize the perspectives from past historical eras will be more prone to be misguided by demagogues and ideologues because they will lack the tools and skills to withstand the imposition of social and political narratives which they encounter.
I am also very intrigued by your theory that history is often turned into a narrative with identifiable with heroes and villains. I would go further and speculate that humans have an intrinsic need, desire, and addiction for narratives; that our species inevitably tries to make sense of all external stimuli, and that our common vehicle of understanding an incomprehensible universe is to turn empirical reality into narratives, into stories which cater to our desire for a) intrigue, b) triumph of good, c) finality & resolution, and d) meaning to our existence.
In this sense, the two doctrines are in conflict: First, that we should unpolemicize history; Second, that humans inevitability tend to "narrativize" history to fit our cultural and societal values. You write, "We wish to find that hero who took on the forces of darkness and forever changed the world for the better. We want it so badly that we will write him into history, running over any inconvenient facts in the process." This seems persuasive. But given that premise, I must ask you whether it is really possible for historians to write histories which are unpolemical? Even if historians are capable of writing unpolemical histories, will they have enough traction to become persuasive to other historians, or even to the general public? Does the structure and composition of History departments at American universities allow the writing of unpolemical histories? Is it possible to teach a course which doesn't implicitly assign valuations to historical events or historical figures? Is it inevitable that historians "narrativize" history? Are there societal benefits to the polemical teaching of history which outweigh an unpolemical approach? Are there benefits to making history into a narrative?
I do believe that it is at least theoretically possible to transcend our human biases and write non-polemical history. The first thing is that history is about a method and not a narrative. As long as we are simply using the historical method to analyze texts we get around the issue of narrative and do not have to worry about bias and polemics. The second thing is that when we do eventually come to write narrative, which we must in the end, we can avoid the standard narratives. Instead of talking about conflicts with heroes and villains we can talk about evolving processes that have arisen between contesting sides. In this, Hegel was onto something, though I would not accept his attempt to enforce meta-narratives over all of history. Even if the two sides may never have been able to reconcile in life, the historian understands both sides and therefore makes a sort of peace between them.