Here's where the notion that social programs can be sustained by immigration from the third-world falls down. It's one thing to be paying to support your own grandparents -- quite another to support people who are not your kin or kith. Add a little Marxist class struggle, stir in a little racism, simmer in a French broth, and you have the receipe for a social disaster.
Another worthwhile take on demographics can be found in the most recent Steyn column. Though it focuses on France and Europe, there are some lessons for the U.S.:
Mark Steyn: Its the demography, stupid