Sometimes you put walls up not to keep people out, but to see who cares enough to break them down. - Socrates quote pp Brief Thoughts On Friendship and Betrayal - Saving More Than Me I can see this in some students.
Quite possibly, this is the cruelest thing that you could do to someone. Particularly when you don't understand it or only know part of the truth (at best), anyway. Let people live; let people learn. (Those are not my words but well said.