It’s “round up”, not “arrest.” Casablanca doesn’t work as a movie (for me), I watch it for the cynicism and ignore the sugary romance and phony francophilia.
It is indeed a cynical movie, that is the whole point, the possibility and even the prospect that even people who are cynical can do the right thing when the chips are down...but of the whole movie, I love the scene where the dueling singing of Nazi (Die Wacht am Rhein) and French (La Marseillaise) songs takes place.
I do love that scene.