Originally Posted by mamabadger
That is definitely part of the problem. Changing the filioque not only alters a doctrine about the nature of God, it changes the understanding of the church hierarchy and the authority of bishops. The idea of one bishop being "above" the others came from this change, leading eventually to other RC beliefs like papal infallibility and the power of the Pope to grant indulgences. When the filioque was introduced, a whole different idea of the nature of the Church was also introduced.
Just to stir the pot a little:
St Thomas, in defending the filioque, said that although it was not originally in the creed, it was implied, and he also felt that the Orthodox theological position implied that the Spirit proceeded from both, though it didn't say so explicitly. (Obviously they would disagree, at least now. I wonder what would have happened if they discussed it before they changed it?)
As far as the Creed goes, he felt that the reason it wasn't originally put in was because the creed was developed in response to specific questions and heresies, and so only included things that were a specific response to those questions. I don't think anyone disagrees that that is how the Creed was framed. However, since (in his view) the words and theology discussed at the council implied that the Spirit proceeds from both, he concluded that it wasn't really a change to simply make it explicit in the creed.
Theologically. according to Thomas, the persons of the Trinity are only distinguished by their relations to the others, which is why the "and the son" is required.