That's exactly why that scene in the movie is so heartbreaking - why it makes you cry as you watch a grown man lose his volleyball. That ball was his lifeline, in a way; it was the only thing that had kept him from losing his sanity, and he had convinced himself that he had a real relationship with the volleyball and it was deep and meaningful to him. He shared all his thoughts and feelings with the volleyball, and the volleyball just "listened" and didn't judge.

I think "emotionally isolated/castaway" is a very suitable term for what a lot of us have felt like over the years, and thus a therapist can easily become our version of that volleyball. I don't see anything seductive about the situation, and have certainly never felt seduced by either of my therapists.