I think the argument is as old as the internet, perhaps even older than that. The scenario should be familiar: a new historical movie comes out, which triggers an argument between two sides -- those that are dissappointed by how historically inaccurate the movie is, and those that claim "it's just a movie."
While both sides of the argument have just as valid viewpoints, I in almost every instance side with those that argue against historical inaccuracy. The point of this blog post then is not to necessarily argue that the opposite viewpoint is wrong or bad, but to explain to that audience why it is important to some people.
One of the points argued is that it's just a movie, and the way I interpret that statement is that it's all just a fantasy, and one should not be too concerned by it. I think this highlights a fundamental disconnect between the two groups in terms of the appreciation of history. I think for the vast majority of movie-goers, the purpose of a movie is to indulge in some fantasy, to escape the drudgery of their every day life and to be entertained for 2 hours. There is nothing necessarily wrong with this desire, but it is important to differentiate how and why people are entertained. One person's epic storytelling can be another person's ponderous snooze-fest.
For someone that has an appreciation of the historical period of any particular movie, the same sort of motivation is also in play, I think. Both audiences want the fantasy, want the experience of going someplace they could otherwise never visit. The real difference, however, is that for someone that is actually knowledgeable of the period in question, the fantasy is broken -- the immersion and the suspension of disbelief are shattered. Simply put, the goal of the fantasy is no longer met by a history fan, and the movie suffers badly for it.
This brings me to a central and important point for the movie producing audience: the cost and effort to make a reasonably historically accurate movie is the same as making an inaccurate one (usually: there are exceptions, such as 300 where an accurate movie could not be made within the context and goal of the movie). Furthermore, those that go to a movie expressedly for the purpose of escapism will not notice or care if the movie is accurate or not: they just want an exciting and well paced movie.
Ultimately, the real reason historically accurate movies are ignored is not because such a movie will be bad (despite the arguments of the detractors; "If I wanted to see a documentary..."), but that the audience that really appreciates an accurate movie is very small, not worth the effort to cater to, and the vast majority of the viewing public, as well as the movie producers just don't care.