Dupe. Nut: there is an actual rule, in place for ages, that disclosure of classified info doesn't declassify it; the notion behind this "warning" is that the students would be demonstrating an inability to deal with classification.
You've never done government work, have you?
Like I said, the rule is probably moot in Wikileaks case, but probably not moot in others. Meanwhile, the classification system does revolve around substituting rigid rules for individual judgement --- and that makes sense, given the sheer number of people who come into contact with CI.