Okay, am I wrong, or did the letter say that this girl knew the guy in question? It sounds to me like they were already friends. If so -- I know that I wouldn't have MY guard up in that case. My little sister doesn't go to frat parties, but if she did and she was invited there by a friend, I would definitely tell her to be careful and watch her stuff and NOT go upstairs with guys she didn't know -- but I wouldn't be all that worried about her going upstairs to a guy's room if they're friends. Who would suspect that your FRIEND is going to rape you? I wouldn't.
Furthermore, if they were friends he probably knew she was 16.
The personal responsibility argument is hardly valid. I mean, yes, you want to take care of yourself -- but if you aren't and you get raped, it's STILL not your fault. We don't hold people who get robbed accountable for the crime because they were walking home alone one evening. We don't hold people accountable for getting hitting by cars just because they chose to cross the street. Why is rape different?
Regardless of whether or not this letter is real, it happens. Do you want me to whip out the examples of sisters and friends I have who've been raped, some of them by fraternity men who decided it was consentual? Because I can do that if Dear Abby isn't enough for you.