Re: May be I will never understand...
Well, talking about universities and relationships, in my university those Muslim brother / sister relationships were not that dangerous, because the worst (According to people) ultimate result people ever came to know of such cases were that their parents intervened on their choice and the result was marriage which they happily and obediently accepted.
The more dangerous were the "just friends" relationships among Muslims. Because a lot of people (Muslims) would try to convert non-mehrams into mehrams by refering to their relationships as "s/he is just a friend" and then all of them used to discuss how much they were impressed from the story of the latest film of that time "kuch kuch hota hai"....etc.. So the ultimate results of some cases turned out to be a bit of impatient pre-marriage thingies and some even ended up with misbehavior with parents when they disagreed to their choice. In short, most endings of such "just friends" relationships were quite worst among Muslims then those "brother/ sister" relationships.
Though I never appreciated or tried any of the above two types for myself, but I always thought the "just friends" relationships lead to more disasters to Muslim pre-married couples then the other one.