Neither magic nor worship of demons leads to the one things which alone is the sign of true piety and to be praised: repentance.
The demons do not intercede with God for man. [Really for a Christian just saying it like that should be sufficient!]
Again, demons do not act as intermediaries between God (or "the gods") and man, not even in terms of conveying knowledge. We must shed ourselves of all of these pagan beliefs. [I'm tempted to draw some kind of reality show analogy, if only to make this stretch of refuting paganism more interesting. But I just don't have the time...]