I was a little kid in the 70s but remember this gung-ho attitude of my parents. Maybe 75 was the tipping point.
They sprung back from 1975 but have been on a downward slide ever sense. If the current trend continues they should have "negative growth" before the year 2010.
http://home.zonnet.nl/rsingelenberg/Web-images/graphs/stats_05/annualgrowth_05.htm