Film is, by its very nature, highly propagandistic. That is, when you read a book, if you detect you're being lied to or manipulated, you can always stop reading, close the book momentarily and say, "Wait just a minute, there's something wrong here!" You can't do that in a film: You're bombarded with sound and images, all expertly crafted to give you selected information and to stimulate certain feelings, and you can't stop the barrage, not in a theater anyway. The visuals and sound and music – and along with them, the underlying agenda of the filmmakers – pursue you relentlessly, overwhelming your emotions and senses.
And when you leave the theater, unless you're really objective to what you've experienced, you've been changed – even if just a little bit.
I think his point is valid; movies lay claim to far more power than we often admit. If we really understood and believed this, I think two things would happen: first, we would have our guard up when choosing and watching movies. We would watch movies actively, not passively, watch them through a biblical worldview rather than passively adopt an unbiblical worldview.
Second, more Christians would go into moviemaking. If it really has this power to change people's minds, shouldn't we be using it for the glory of Christ? Hopefully, Christians in moviemaking wouldn't be underhanded about the change in view they're trying to effect, as most movies are.
You can read the article here, but please be warned that it contains some fairly graphic language about the movie.