As the guy who helped Serak develop his theory on the drive back from the DC signing, I can unequivicably confirm that, at the creation of the thread, there was no WoJ as to wether Fitz was cursed or not. That statement was placed in the OP as a clue for the rest of the forumites as to who we thought his parents were.
Insofar as Fitz' red hair and pug nose, we reread Fool Moon looking for physical descriptions of McFinn and discovered that his human discription had been painted with very broad strokes, invoking everyone's personal image of a rugged mountain man without actually going into much detail. The red hair and pug nose are treated as clues because both have become steriotypes of Irish decent, not because they match McFinn's description.
Another avenue that may or may not have been fully explored in the past 15 pages; who exactly did Saint Patrick curse? Irish legend mentions a mage/king by the name of Finn McCool (or Finn son of Cool.) Finn McCool was known for having preternatural wisdom when he accidentially tased the Salmon of Knowledge as an apprentice wizard and was said to have dealings with the Tuatha de Dannan. When expanding through Europe, the Catholic church was known to attempt to discredit pagan leaders to bolster the faith of their local converts. I find it plausible in the DV that either Finn or one of his decendants would be targeted by the church as a living reminder of benevolent (or at least powerful) forces outside of the christian pantheon. In a move to secure the catholic faith in Ireland, St. Patrick cursed the Island's previous supernatural defender to become a ravening beast, forcing the people to turn to the church for protection.
Please keep in mind that I am in no way trying to condemn or condone any historical actions of the catholic church. The church of 1200 is different in many ways from the church of 2011, and I am talking about a fictional universe.