OURTorah,
We had a class discussion about this a few weeks ago. I expressed my view on the matter, which incidentally was the same as yours, and my teacher explained why it’s better for most BY girls not to go to secular colleges.
You and I both grew up in open minded homes, by which I mean to say that we were exposed to secular culture somewhat. So when some random dude would ask us if we want to study for a test with him, we would know how to politely refuse. Whereas a sheltered BY girl that has never spoken to a male other than her immediate family members would find themselves unable to turn the guy down (guys can be persuasive of need be…)
The same would occur if someone would ask a BY girl a question on Judaism. Firstly, she most probably wouldn’t know what to answer, as BYs generally don’t give kiruv classes to their students, and second, she would end up getting into a conversation, and possibly an eventual relationship, with whoever asked her the question.
My teacher said that she knew of many cases like that.