Abstinence denial refers to two phenomena, deliberate denial of the efficacy of abstinence in preventing disease by liberal and pro-abortion groups, and denial from ignorance by those who have been convinced by the propaganda.
Groups such as Planned Parenthood have enormous interest in promoting sexual promiscuity, as their profits rely on it. Likewise, pharmaceutical groups selling drugs such as Gardasil and various forms of birth control cannot profit when abstinence is used.
The liberal entertainment industry relies on immoral consumers to purchase its products with immoral sexual content (television, film, etc.) Denying abstinence's efficacy is thus part of a wider attack on Christian morality.