It should be reasonably possible to ascertain whether you and your spouse will have a pleasant or unpleasant future. If the latter, why the fuck (pun intended) would you have children?
Protracted job loss? Major illness? Death of a child? War?
There are a lot of variables that go into the success of a marriage that can't be predicted, especially over a 20+ year timeframe. The idea that you can reliably predict if someone'll be happy in their marriage decades later is... unsupported.
Who can do this? Who can possibly guarantee anything about the future, especially when it involves other people?