Why buy the cow if the milk is free?

“Why buy the cow if the milk is free?” 

I actually heard a song with those lyrics on the radio today.  Okay, it was a spoof on country songs, but it reminded me of what our adult leaders said to us as teens when they talked to us about S-E-X.  They usually spoke in DaVinci-like code — all mysterious and whispery — while never actually saying the word…well, you know…