Reading Mr. Chuck Colson's "Europe's demographic crisis," it becomes easy to see why a marriage is intended to be a "fruitful" union. Children are intended to support their parents in their old age. This bit of Catholic morality is so self-evident that it is even built into the assumptions behind the welfare state. While these services may appear to be free, it is important to remember that the doctors and nurses are not working for free, and that medicines still cost money. You simply pay for them through your taxes. Thus as people retire and pay less in taxes, their needs are met by the taxes of their children. Thus they must have had sufficient children for their children's taxes to pay for both their own needs and the needs of the retired generation.
The quick retort that I tend to hear is the example of a French or Spanish citizen who lives here and goes "home" only for medical reasons. Such a person pays little or no taxes there, and so gets "free" medicine. Cheating the system in this way is certainly possible. But its also certainly not an option available to everyone. What do you do if you get hurt to badly to fly home here? And what do you do when everyone at "home" is too young to work or too old to work, and thus is not paying much in taxes? Where is the government going to get the money to pay for this? Clearly such examples are simply exceptions, they cannot be the norm, and so do not disprove the generalization.
Colson, Chuck. "Europe's demographic crisis" BreakPoint Online 2005-07-11 http://www.townhall.com/columnists/chuckcolson/cc20050711.shtml