People are rarely as bright as you hope; nor as stupid as they seem.
Re: Rush Limbaugh and Sandra Fluke.
Mark Kleiman checked into attitudes toward premarital sex by age and party. The significant results are that while 71% of those 18-34 think pre-marital sex is acceptable, only 47% think so. This coincidentally (really!) matches the 47% of Republicans who find it acceptable.
Given what we know about Limbaugh's audience, he is talking to people who agree with him. He is giving voice to what they are thinking.
I am of that age. I remember the intensive training that I in the public schools for abstaining from sex until marriage. Many admonitions on that subject entered one ear and quickly sped to the other. My sterling record of teen sexual abstinence does not prove that the propaganda was effective.
The opinions of those over 55 about pre-marital sex are irrelevant. It is not a choice that they face. For many, their opinions are just what they decided at that time of their lives. That the current cohort are so narrow-minded testifies to the pervasive repression of the era they grew up in -- the hypocrisy of the Mad Men era. Many people over 55 suffer a kind of PTSD from the slut-shaming (and gay-baiting) culture of their teen years.
None of this explains how a man who has been married four times has such limited knowledge of how modern birth control works.