Oh well...let's agree to disagree. I just think if it's on the screen...or rather an actor...it should have a purpose that serves the script.
The script is only one element in creating a film. The purpose of much of what's on the screen in any film is to go beyond the script, to create a world
. To sell the illusion that the story doesn't simply exist in a vacuum, but is taking place within a larger reality.
Sometimes in a Law & Order
episode, you'll see the cops wearing black mourning bands across their badges, even though there's nothing in the script about a cop being killed. Is that wrong for them to do? Hell, no. Because it makes sense. New York is a big city, with far more going on in it than any one show can depict. Knowing that a police officer was killed recently may have no bearing on the script, but it contributes to the illusion that the show takes place in a larger, credible world, that there are things going on in that world beyond what you see on camera.
Limiting yourself to the script alone is the worst thing you can possibly do as a filmmaker. The script is just the beginning of the process.