BT2, I agree with what you say about this being like a syndrome. The therapist has as much ability to influence their adult client as a parent has to influence the developing heart and mind of their young child. It would seem that the bond between therapist and client is forged in the same soil as the bond between parent and child. We could possibly liken the process to footprints in concrete, the unmet needs within us are like concrete that hasn't set. The therapist is able to reach into these unset places within us, places that our parents neglected reach, and are therefore able to set their own prints indelibly within us.
As you observed with your friend, its not just the therapist who can do this - it could be anyone who manages to inadvertently tap into these unmet needs and plants their foot there first. But the therapist has a unique advantage, like a master navigator, they know how to get to these unset places, they understand the properties of concrete and they know how best to set them. What an amazing power the therapist has, and an incredible amount of responsibility.

It certainly makes you wonder about the psychological and emotional state of the therapist, because this affects the shape of the imprint they leave on us. We assume they are healthy - but what goes on in the mind of the therapist who abuses this power over their vulnerable clients? The therapist must be driven by needs too - and it would be a very interesting study, possibly already attempted, to explore what drives and motivates the the therapist in this instance.