Yeah, the teacher is behaving in a very contradictory manner here, I agree. "Do not censor yourself" and "but I'm going to have you arrested for your violent and disturbing essay" probably translates to "the quality of work turned in by future students will suffer." Also "I don't really mean don't censor yourself, but it sounds good." (It's Jerzy Kosinski, Mug, so you were quite close.)
Now, a session or two with a counselor of some kind mightn't be a bad thing. I'm not one of those who thought the VT shooter's writings should have necessarily been "warning signs." But often--not always, but often--such writings are a sign that the person writing them is going through a rough time or having some kind of emotional trouble. Then again, the editor of my high school's literary magazine my sophomore year wrote a lot of this sort of thing. (I know; it had been my job the year before to read through reams of his stuff to pick out a few items for publication.) He was quite well-adjusted, but he had a thing for Dean R. Koontz and Stephen King, and he tried (badly) to emulate their style.
"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"
"You can't erase icing."
"I can't believe it doesn't work! I found it on the internet, man!"