It's not universal enough to be advised to someone as a solution, increasing the already existing social pressure to have children, and also exposing both the potential parent and child to the risk of lifelong unhappiness together.
Also "spouse or children" – those are too different, Personally, I've been married for over a decade, but I don't have the emotional capacity to be a parent and desire to have kids in the first place.
>You seem to not know anyone who was an unwanted child born because of some secondary motivation
Don't you think there's a difference between suggesting that someone start a family (and itemizing benefits of that life path), and FORCING someone to start a family? If OP does not want a family, they don't have to have a family. Geez.
You are the one aggressively pushing others to have kids with unproved statements that only a minority is not cut out for this task and that it will surely give them purpose. So the kids will become a means to an end, in your own words: "a solid reason why you should get out of bed".
This what leads to deeply affected people: being born and raised because the parents had some secondary goal in mind and needed children for that goal. Can be searching for meaning in life, social pressure, material benefits or even "our beloved first child needs a sibling".