There are several reasons why alcohol increases the likelihood of sexual assaults. The National Institute of Justice identifies the following factors, to which I'll add some of my own explanations:
Alcohol use can lead to increased aggressive behavior -- so a person who might otherwise act respectfully toward others can become sexually aggressive.
Alcohol use inhibits a person's ability to interpret another person's behavior and signals. So a man might think a woman "wants it" when she really doesn't, and when she says no and tries to fight him off he'll think she's "playing."
When on a date, alcohol use makes both men and women more likely to think that sex will be a part of the date. Though both may begin the date with that thought, it then can also happen that one person doesn't have a desire for the date to end in sex, but the other insists it will.
Alcohol consumption makes individuals take risks they would normally avoid. So a woman may not safeguard herself the way she would normally because she's under the influence of alcohol, and be more in danger of becoming a victim of assault.
Alcohol can undermine an individual's capability to resist sexual advances or a sexual assault. If a person is in an intoxicated state, she may become unable to fight back or remove herself from an assault situation.
A mass society is a society in which traditional social ties have been diminished due to prosperity and bureaucracy. According to the Mass Society Theory, the increase in size and modernity weakens the social fabric and individuals become more individualistic and socially isolated.
