Because some misguided fools are still in the Dark Ages.
There was the case about 3 months ago in Chicago where the pastor (church worker?) sat on the 4 year old boy to 'cast' the demon out and the little boy died of suffocation.
This is ridiculous.
And I don't want to accuse, but I am going to anyway, it is the fault of fringe churches. It is your idiot, fringe, Baptists, Pentecostalists etc. that really believe all this crap. The mainstream Christian churches left this mumbo jumbo behind 100-150 years ago but the fundamentalist nutcases (and show me one who isn't) still rabidly believe the demon nonsense.
I know freedom of religion is one thing, but murdering a child is another.