What you've just witnessed, of course, is how the Pattersons reject common sense and substitute their own arbitrary, silly and stupid point of view. The example I came up with, of course, doesn't appear in the strip itself but it's the only thing that doesn't involve Elly having super OCD that makes sense; what could have happened is that she watched Marian do a lot of laundry and never stirred herself to ask why because she assumed that's simply how things were done. If so, her need to not assert herself when it's necessary acted to her detriment once more.
Also, her inability to see that simply because a dog has an expression on its face that means a certain thing when it's worn by a human doesn't mean that the dog feels that way hampers her almost as badly as her belief that if she demonstrates her sincerity, her children will sit quietly where ever she plops them and not do anything baffling like move around or get into things. In both those cases, she would rather not accept the fact that a dog doesn't think along the same lines as we do or that a child needs more attention than she has the stamina to provide.
Similary, John cannot get it through his thick skull that when he makes his demeaning remarks, he will not be applauded for his creativity; the idea that his right to swing his arm ends with the other person's nose is seen as an attempt to limit his right to swing his arm. He also tends to not be on the same page with the rest of us when it comes to asking the question "What's going on around me?"; a man with a lick of sense would ask "What really happened in Anthony's marriage?", "Why does Elly look so unfulfilled?" or "Hey, I wonder what's got April so upset about the move" instead of letting his preconceptions answer the questions for him. That way, he could avoid the baffling horror of being blindsided when truths that he never foresaw because they don't mesh with the shibboleths spot-welded into his narrow mind emerge. If, for instance, he were to come across proof that even he could not will away or shout down that Thérèse was far more sinned against than sinning, it would totally throw him for a loop because, despite being an unavoidable reality, it would same to make no sense at first.
Having to answer the questions the revelation of what an awful person his beloved Anthony really is raised would, of course, occasion the same sort of unpleasant conversation Elly has with herself whenever she does something so dumb, even she can't hide behind the old, familiar excuses; the nasty little voice in his head that tells him that he doesn't actually know anything useful about anything because he refuses to think about what he's doing would be roaring back with an unwelcome vengeance.
When the time does come for John to realize that most of what he thought was solid, unshakable fact was in reality as fragile as tissue paper, he won't be able to deal with it any more than Elly can really admit that she wasted her life chasing delusions. It would be like the terrible day when Liz is somehow forced to face the fact that it's not the world's fault that it doesn't supply her with an endless supply of ankles to cower behind in diaper-soiling terror; I don't even want to think about the day when Mike realizes that he's wasted his life expecting everyone to service his needs.