Let's face it: professing a deep interest in movies, the absolutely dominant global art form of the last century, is at this point like professing an interest in air. Passion is nice. Erudition is admirable. But it's like that moment when good manners cross over into meaningless etiquette.

This quote is suggesting that saying you have an interest in movies is not special or unique anymore because everyone watches them. It is like saying you are interested in air because it is all around us and no one would be surprised because of its ubiquity. It also insinuates that having more knowledge about movies, or “erudition”, is not that important any more either because everyone can watch them. Thus, this quote is saying that having a passion for movies is nice, but it is not something that will make you stand out.