I suppose there is an appropriate range of responses. I have a negative reaction because my teenager has nightmares just from hearing about this sort of thing, even without graphic details or pictures.
However, if the students in this situation were traumatized, they certainly could have stopped watching!
I only saw a few of the stills and that was enough to "inform" me - in as much as I can be informed.
What I saw was enough to remind me the fight against extremist islamite barbarians will be to the death of them. Only a well informed society can effectively come to grips with that reality and to teach highschoolers anything else and/or to insulate them from the evil will only be to the young's future peril.