To me, the notion of marriage flies in the face of this basic observation. How can you possibly commit to spending the rest of your life with someone when you know so little about how they will change, intentionally or not?
> The 'think of the children' argument is pretty strong here. We all know the stats: kids from single-parent families tend to grow up in more negative environments, tend towards worse outcomes.
This sounds like selection bias to me.
At present, in Western society at least, members of certain socioeconomic classes are significantly more likely to become single parents, and it is likely the socioeconomic conditions their children grow up in that have the most significant effect on their outcomes.
Conversely, abusive relationships and unhappy marriages also provide negative environments for children to grow up in. A future in which relationships are more fluid could reduce the number of children growing up in these environments.