One point made by a historian about 20 years ago was that, for all the horrible historical films that have been made, people nowadays have a better knowledge, including visual references, of history than, say, 50+ years ago. The reason for this was that in the past only "serious individuals" studied history, while there is a greater readership of historical novels (of widely varying degrees of accuracy) and watching of historical films and tv shows. Yes, he also pointed out that it was also very hard to remove the misinformation that cropped up in such films (most of them have something basic wrong, many of them are wrong from beginning to end), but there are more people who recognize Roman armour, for example, and the like.

Historical films are a two-edged sword. Most people go to films (or books or tv shows or almost anything else) to have their point-of-view confirmed. Most people do not want to have their views challenged. Even when they learn something "new", they want it to fit into pre-concieved positions and attitudes. Therefore you could make terrifically accurate films, but probably very few people (other than a few scattered historians) would want to see them. Conversely, you can do damage to the history and then hope that the audience comes away with at least something and do spin control later. I'm not sure which direction is more useful.

People have been spinning history and using it in a wrong-headed manner since we first started speaking, much less writing. The situation in the world today is a reflection of these wrong-headed ideas about history in general... :-(