I thought it was a bit crappy that Leslie refused to marry the pregnant Daphne, and his mother was happy to go along with that. At that time (pre-war) even in England, but especially somewhere like Greece, that would have pretty much ensured her life was ruined. By becoming an unmarried mother she would have been disgraced forever, and probably nobody would ever have married her.
It would have been understood that the honourable thing to do would be to marry her. If he was too young and not ready for fatherhood, and not in love with her, tough luck, should have been more careful!
I think the writers are imagining it is happening nowadays, when society has changed.