“One in three women who drink almost every day reports having had sex with someone the first time they met, a number even higher than their male counterparts (at 29 percent).” (91)
“drinking does have a strong, linear, and enduring connection to the formation of casual sexual relationships: the more alcohol, the greater the likelihood of sex.” (280, n. 11)
Their research shows that young women who were sexually abused or strongly pressured into sex in high school or younger are more prone to casual sex or to sex at the beginning of what they hope will be a relationship. We know from other research that fatherless girls are more likely to turn to sex earlier and with older men.
A running theme of Premarital Sex in America is that emerging adults follow a small number of standard "scripts" about sex that shape what they think is normal. I think that some young women follow a script that says that casual sex is a quick way to get men to pay attention to them (which is true). But they also experience that casual sex and broken relationships hurt them, even if they try to tell themselves that it shouldn't.
Putting these facts together, I think young women who follow the casual sex script, even though it hurts them, use alcohol to self-medicate against the pain that their script - their lives - are causing them. Drunkenness provides a socially understandable excuse and fuzzes their memory of what happened.