1942 Ethical Standards

We can assume that “not suitable for general exhibition” was roughly equivalent to what an R rating means today. (Or used to mean). What in Casablanca could have given moral guardians this level of concern? Probably the allusion to sexual relations outside the bonds of marriage between Richard Blaine (Humphrey Bogart) and Ilsa Lund (Ingrid Bergman). What else could it be?