The theme is When civilization does not exist, humans are susceptible to change, going from good to evil.
I think if the Director and producers really wanted to make an effective version today, they could. The trouble is that studios want to put out a movie that will make them the most money possible. When classic books are source material, producers tend to stay clear of details that they think will not sell well to the general public. Any worth-while version of LOF would need to focus on the beast being the inherent darkness within the boys. The movie would need to spend more time on Simon's character as both Christ-figure and truth holder and juxtapose these traits with the rest of the boys who have gravitated towards darkness to varying extents.
