No one ever mentions sex when it comes to conversations about declining birthrates in the western world. Its always very abstract discussions (immigration, free personal time, etc) around the main issue. No sex basically means no babies. It seems there is a latent western sexual crises no one wants to talk about.
We have gobs and gobs of sex. What we usually don't have are gobs and gobs of children. Whether that's good or bad I think reasonable people can debate.