Women on birth control are sluts. Limbaugh was attacking Sandra Fluke, the law student who was denied the right to speak at the congressional hearing about contraception. Skip to the 3:00 mark for some truly terrifying insight into how he believes women should be treated.
In summary, Rush Limbaugh believes that somehow wanting your health insurance to cover contraception is the equivalent of admitting your sex life is so active you have no time to go to work and make enough money to pay for it yourself.
He believes that 40% of Georgetown's female law students are sluts promoting casual sex/prostitution.
He believes there is no purpose for birth control outside of wishing for consequence-free sex. That it does not have medical uses unrelated to pregnancy prevention.
He believes that the President should force these "sluts" into marriage whether they like it or not and they should be kept at home and pregnant until the end of their days.
These are things Rush Limbaugh believes.