PPs referencing those in poor countries having children to ensure there is support in their old age - indirectly, it's the same here, it's just we look at it from the point of view of money from taxes paid, rather than hands on support. We contribute to our communities as a whole financially rather than physically.
Not only do we have an ageing population, we also have generations coming through who will not be starting to make those financial contributions until later. The percentage of net contributors is not really being increased by the number of people now remaining in education.
All that is happening is that the number of mass contributors is reduced during the period in which the next generation is still in further education/part time employment.
Whilst the importance of net contributors can't be ignored, the fact is the majority are not and never were net contributors. But they will still BE contributing. We are now in a situation where the majority of our most able mass contributors aren't contributing at all until at least 6 years after the majority of previous generations would have started.
Whilst people are now expected to work longer at the other end there are fewer guarantees of health into our late 60s and beyond. We can't just keep shoving the pension age up. At some point we really need to bring the working/contributing age at the other end back down, unpalatable though that might be. And the problem there is that there are fewer and fewer employment options for unskilled teens. There isn't the industry there once was. I still believe the push to get young people into higher education has more to do with massaging unemployment figures than wanting our kids to have opportunities.
We need more young people in full time work from the age of 16, but we no longer have the work for them, certainly not work that will pay them enough to live on in the future.
I don't know what the answer is, but I don't think simply having more children is the solution to the Western problems caused by the drop in birth rate unless it is accompanied by much reduced public services and effectively turning the clock back to a time which wasn't dissimilar to those nations today having children to physically care for the older generations, etc.
And how many people will go for that?