As I've said before on this very blog, the John of the early years was, to say the least, uncomfortable with the idea of Elly getting any sort of work out of the home. The reason that he gave outsiders was that if a household didn't conform to the 'Man-breadwinner-Woman-happy-homemaker-content-to-stay-home' model, it wasn't really a home. He said this to his working mother assistant Jean and bridled at being referred to as a chauvinistic anachronism; the subtext given was that he sort of knew he was wrong to hold Elly back but was too entrenched in his macho position to admit that he was being a selfish son-of-a-bitch. In his mind, he had to assert authority and treat her like a simpleton lest he be regarded as a failure. As I have also said, there's a problem with that theory: Elly is a hopeless incompetent who has no stick-to-itiveness. Anyone with a brain can see that what ever she starts, no matter how enthusiastic she is about is in the beginning, she fails to see through; when, as always, she quits out of boredom and frustration, she shrugs and makes some sort of lame excuse. It would be a kindness to keep such a person out of sight so they don't publicly humiliate themselves so his discomfort has an explanation that fails to serve the purpose of demonizing Rod for making her stay in the small town she hated: chivalry. Good thing for Elly that she hates the idea of being helped; if she were to twig to the fact that John is trying to protect her, she can be enraged that he has no faith in her.