Casablanca looks nostalgic today because its look has been copied so many times and because it's Time Past now, but when it was made in 1942, it was the present and fictionalized a moment in time that nobody alive then would ever forget. Anybody in my older generation family who had been an adult at that time had some sort of story parallel to that, a moment in time when the world changed and personal life was overtaken by events. Casablanca was light on horrific details because audiences were confronted on a daily basis by reality and wanted some sort of escape that was personal, romantic but not graphic. I can easily imagine a plot line from some peripheral spin-off stories of the refugees who occupy the background in the plot line.
There is a tendency to gauge old movies through the lens of today's fashion and mores. Using that yardstick most older films are going to seem a little silly, irrespective of the high quality that went into many of them.
Imagine if audiences from prior eras were somehow able to see the films being made today. I think they'd be confused and often repulsed.
Personally when I look at truly old films, e.g. the silent films and the earlier talkies, I try to consider the techniques and artistry of the time. Sometimes there were subjects and opinions presented by the filmmakers that went against my own beliefs, just as there are today, but I try to put those aside so as to appreciate the film in its totality. But Casablanca is not one of those. I enjoy every minute of it...