On kicking students out of class

As someone who spends a portion of each weekday on a university or college campus, I've been thinking quite a bit this week about the coverage and about the incident itself: the emphasis on the shooter's ethnicity, the way, as David Brooks discussed in yesterday's New York Times, that we don't look at these sorts of incidents as moral failings, but as psychological or moral ones, the danger I am in when I teach a class, etc.
But another thing that has struck me is the rush to blame someone in the University administration for not having done something about Seung-Hui Cho's--I'm putting the family name last here since I'm not going to be considering primarily as a South Korean, but as a product of the country he grew up in--behavior earlier.
As I said, I am on college campuses most days. And, I see students, and have had students, who are of questionable mental health. I know of students of mine who have spent time during their college careers being institutionalized. I have read student papers that are dark, frightening and demonstrate an imagination, at least, that is somewhere I wouldn't want to be. But, as much as we wish that Virginia Tech would have stood in loco parentis in this case, we don't feel the same way in every case. I'm pretty sure that the same people who are now asking why Cho wasn't kicked out would be upset if their own child was kicked out because he creeped out other students and faculty--but never enough that anyone pressed charges. I'm not saying, because I don't know all the details, whether Cho really crossed a threshold so that it was already clear that he might go on a rampage. I am saying that were we to get rid of every creepy and troubled student, there wouldn't be that many left.
Whichever way the ultimate judgment comes down on Virginia Tech authorities--how well their police handled the interim period between the shootings is a different question--we should remember that hindsight is ever so much clearer than foresight.