Why are the Persians is the movie "300", depicted as sub-human?

Why are the Persians is the movie "300", depicted as sub-human? In creating a movie based on history, do the film makers not owe it to those who the movie is about, to depict them as most historically accurate as possible? Yes, I am aware the movie is about Sparta and Spartans. But I think depicting the Persians as sub-human mosters is disrespectful to an entire race of people and undermines their contributions (which are quite many) to the World as we know it today.