Again human decency. Most moderate modern insert religion here follower would probably not be okay with showing such graphic images to Elementary aged (or even High School aged) school children. If I'm not mistaken American Elementary only goes up to grade 5 before middle school starts? That's way too young to be exposed to topics like abortion (homosexuality maybe if they ask) never mind showing this crap.
I would hazard a guess that they would find this appalling to their beliefs because one it demonises people as unsavable and two distorts the teachings of Jesus. It is literally a show of human judgement and humans taking vengence, which is God's alone to do so.
An eternal Hell might be a fear tactic but believe it or not, not all Christians would support such a message instead preferring to emphasise the forgiveness of Jesus and God's love.
How does it distort the teaching of Jesus when he talked all the time about Hell? You could easily turn many of his parables into Hell House stories.
It isn't love to hold a gun to someone's head and say you will pull the trigger if they don't accept your "forgiveness", so how can it be love to even have an eternal hell in the first place?
And so again, it's hypocritical to be against the Hell house, but not against Hell in of itself.