I looked up IFS on Wikipedia (to get a short overview). It sounds like it would fit into anyone's good understanding of what happens with people, and is similar to the effective parts (!) of any therapy.

There is one sentence on Wikipedia that got to me (as the same thing always does):

"IFS explicitly recognizes the spiritual nature of the Self, allowing the model to be helpful in spiritual development as well as psychological healing."

I simply do not understand what the distinction is supposed to be between "spiritual" and "psychological". Unless it means a belief in God. Seems to me that is what is implied.