From divorces among family & friends - yes, those concerns exist. But they are also worst-case scenarios, and there are many "friendlier" divorces. Or divorces after the kids grow up - where none of the paternity, left-to-raise, and visitation issues really apply.

Vs. even if marriages were magically 100% secure - the costs of having kids in most modern societies have skyrocketed over the past half-ish century or so.