Steve, I used to agrue this point with one of my supervisors. He swore that if the individual got healthy s/he would be rejected from the family by the "forces of homeostasis". I reasoned that it could work the other way -- that a healthier individual would be nicer and easier to be around and could in turn have a health inducing effect on the family. Because of the supervisor - supervisee power differential I "let" him win the argument. Years later I read "Dibs In Search of Self", and found out that I was correct all along.
Using trance logic, the supervisor AND I can BOTH be right. The outcome could go either way. I guess the lesson is for therapists to try to remain aware of the impact that our work with clients can(will) have on many others outside the therapy session.
Woody Guthrie wrote "All I know is I add up all I know, and I still don't know."
Regards. LPM