Huh? Where did you get that idea? Seems to me that you are cheerleading for societal breakdown. What societies have flourished when its people stop honoring marriage and family?
From the children of current friends and co-workers, from my memories of college classmates, from children who I used to know when I coached gymnastics, and from the revolving cast of college students to whom I've been renting rooms for the past 15 years. Not all children are miserable when the parent they live with acquires a new significant other. Some are quite happy about it. And a few end up being even closer to the new significant other and/or step-parent, than to either of their own parents. You may regard my position as cheerleading for non-traditional family structures, but I can just as reasonably regard yours as cheerleading for the failure of any alternative family structures. If children and adults are constantly bombarded with the message that they're supposed to be miserable if they don't live in a married-forever-with-children family, they're a lot more likely to be miserable, than if they weren't getting bombarded with that negative message.