The words wrap a rainy-night encounter in real warmth, a lonely stranger and one perfect night, then reveal she used him to conceive a child and slipped away without a word of it. You start absorbing a template where deep need can justify using another person without their knowing.

Run this and the deception hides inside the romance. The warmth of the encounter makes the using go down easy, so the part where a man is turned into a means and kept from his own child registers as bittersweet rather than wrong. What sticks is the sense that wanting something badly enough can quietly excuse how you get it.

When a population runs it, using another person for your own ends, here a stranger deceived into fathering a child he is then cut off from, gets softened into a bittersweet romance rather than named as a wrong. People start absorbing that tenderness in the telling can excuse deception in the act.

What erodes is the baseline that people are not instruments. A culture running this gets practiced at feeling for a sympathetic deceiver and slow to count the cost to the one deceived, so consent and honesty quietly drop out of the picture when someone's need is strong enough. The trust that frays is the assumption that a partner in intimacy is a person, not a resource.