When we realize that the ancient, pre-Christian world was filled with stories about superhuman gods, goddesses and heroes of all cultures whose purported lives on Earth were replete with miracles of all manner, we must recognize that it is only by extraordinary human perseverance that one particular set of fabulous tales from one particular culture has become accepted as "true," while all the rest are deemed "myths."*
This is not excatly what happened. For centuries Christians continued to believe Hercules had lived and been very strong (probably killing monsters), denying only he was a son of Zeus. Debates have been made on whether demons are able to make children and how (pertinent if Hercules story is taken as otherwise true, or when it comes to Merlin), and St Thomas Aquinas basically attributed such births to "insemination by evil angelic gynecologist" as he thought angelic beings in themselves had no couilles or other production of semen.
Myth in antiquity did not primarily mean untruth, or made up story. It meant the story was told straight off with few details and no investigation referenced by saying "this source says so, others say so, I believe only this is possible ..." as the historians would do when telling a story.
What Christians came to believe in the North was not that Odin had never appeared or made apparent miracles to convince Swedes with their/his descendants in Norwegian Royalty too. What they came to believe, what we find in Snorre, is that Odin was a magician versed in black arts.
In short, Christianity did not teach men Paganism came exclusively from human fantasy, it taught them the devil had finger in it.
Bibl. Audoux, Paris
St Anne's day
*Truth be Known News, Tuesday, May 26, 2009
Is Jesus a Myth?