I think it is difficult to get one's hands around this problem and there are many factors: No-fault divorce is one. The ease of travel and consumerist lifestyle is another. A third is high taxes and the high cost of living. It will be interesting to see how this plays out.
Of one thing, I am sure, though. The country, as a whole will drift "rightward" as time goes on. Conservatives are more likely to have babies (and not abort them) and religious conservatives are more likely to have more babies.
Conservatives have more legitimate babies, granted. But not more babies overall, IMO.