I'd like to start off by saying that before I even knew about the term "film noir", films like It's A Wonderful Life and the Maltese Falcon were staples in my movie library. In fact, I am always one to argue that, while I do enjoy watching It's A Wonderful Life during Christmas season, the film is so much more than a Christmas film. I feel like that is so lost in this day of age where the film is on constant repeat, but only during the Christmas season.
In fact, I'd be more willing to argue that the film is simply a "Film Noir" that takes place during the Christmas season. For example, the film is not a by-product of the season it takes place in. What I mean by this is that, while a film like the Frankin Bass Rudolph the Red Nosed Reindeer requires that the film take place during Christmas, films like "It's A Wonderful Life", or more recently the horror film "Gremlins" and the sequel to the beloved Ivan Reitman Ghostbusters film, "Ghostbusters 2", take place during the season but could just as easily take place during any other season and the film would not loose any of its overarching themes.
I believe my argument actually goes a long way in proving the opinion of the lecturer in our first video lecture. He states that he doesn't believe that "film noir" should be classified into any specific genre. A "Christmas film" such as It's A Wonderful Life could just as easily be considered "film noir" as a "action/suspense" film such as The Maltese Falcon or the James Cagney gangster film "The Public Enemy" could be also.