I think the re-emerging pope in MTW was a good thing. Some seem to not understand how important a figure he was to people of the era and how many people were far more loyal to the Church than their state.

It is definately believable that, if a king attacked the vatican, people from all across Europe would volunteer to fight for him with the same religious zeal as they did in the Crusades.

I hardly ever attacked the papacy in my MTW games, as it just isnt believable.