As a child of a mother who cheated and ruined our family, I complete agree with you. This story filled me with disgust, and I want to live in a culture where people like this feel guilt at what they did. The sibling response here is happy to tut-tut you with the weight of progressive cultural authority behind them, as only a short sighted ideologue could. Lying of this level is bad for the family and bad for society. Protecting it is akin to protesting the removal of a cancerous tumor.