>Can't think of a worse reason to have children.

Then you lack imagination. Unfortunately, there definitely are worse reasons than civic or religious duty to have kids. Having a child because you think that it will save a failing relationship, for example.

The upside of framing it as a civic or religious duty is that it helps build the village around the family. When the rest of the community (political or religious) accepts that raising the next generation is an important obligation, it changes the mindset about helping, and parents can't be islands. Extended social support networks matter. Those communities are more likely to help with something that's a duty than something that's a personal choice (kids as vanity possessions).