Every individual is going to have their own take on a film and read into it whatever they want, but i do struggle to see how anyone could consider the Exorcist to be carrying some sort of negative aura along with it. It's ultimately a film about faith, right?
Blatty believed that a story about "what happens in these cases could really be a boost to the faith. It could show people that the spiritual world is real."
Shortly after the movie opened, a Jesuit priest told him that he witnessed a "thundering herd of people headed into the confessionals" and Blatty was delighted by that, because his original intention was always to reinvigorate the notion of 'faith' by writing an "apostolate of the pen."
Although the surface fireworks rest on elements such as the possession of a little girl and defilement of the family home, the real crux of the story is Father Karras suffering and fighting through a crisis of faith.
"Karras has started to doubt his own humanity," said Blatty. "He is the ultimate target of this demonic attack. The devil is tempting him to despair."
In the novel, it's made explicit that "...the point is to make us ... see ourselves as ultimately bestial, vile and putrescent; without dignity; ugly; unworthy. And there lies the heart of it, perhaps. For I think belief in God is not a matter of reason at all; I think it finally is a matter of love: of accepting the possibility that God could ever love us."
By the end of the movie, Karras has come to let go of the near all-consuming guilt and grief he feels over his mother and which has led him to doubt that he (and people in general) could ever be deserving of Gods love. Only by coming face to face with pure evil was he able to reopen his eyes, rise above rational doubts and take a (literal) leap of faith....right out the window like, but never mind.
Blatty's (perhaps naive) hope was that, after it had all sunk in, moviegoers might see beyond the surface shocks and special effects to find themselves following a similar spiritual path to Karras, or at least come to contemplate some of the same questions:
"My logic was simple: If demons are real, why not angels? If angels are real, why not souls? And if souls are real, what about your own soul?"
Then again, i could just be talking out of my ass. I mean, i'm not religious at all, so what do i really know of the reasoning behind it? Maybe I'm just excited at the prospect of Rainman pulling off a possessed, pea soup pewking, pre-pubescent with a 'potty mouth' and i'm eager for people to not put a dampener on it's potential realisation?
As for 'explaining to kids'? I'd just use it as a cautionary tale: 'Either cut the crap and get yourself to bed or THIS is what you're going to turn into....A junior version of Jackie Stallone'.
