I'm simply challenging the notion that incidences of sexual assault are much higher than what is reported right now. And these things I mentioned enhance the likelihood of sexual assault, but they certainly aren't a direct cause (which is what I think you are arguing).
You also can't say they don't play a factor in the number of sexual offenses that occur on a campus. Alcohol/drugs lower inhibitions and block the ability to draw out potential consequences of our decisions. Yes, most sex occurs at night, but the rape/assault incidences I refer to are often due to a girl walking alone at 3 am from a bar and getting attacked. I agree with you about the frat/sorority link - it provides a setting for parties, drinking, and devious behavior, but that doesn't mean BYU students couldn't find a substitute for that somewhere else (minus the drinking, obviously).
And I agree with you that the Honor Code isn't the main reason sexual assault occurrences are lower at BYU - it's that the students are LDS, and have values they commit to and believe in.