You raise one of the most important points at issue now in the therapy world. As I have written, there was a good reason for the classically trained psychoanalyst to adopt what we tease as the "frozen turnip" style of expressionlessness. Psychoanalytic theory taught that emotion was the result of drive energy going to the wrong place, and excitement could appear only when the sexual drive hadn't been processed properly. Thus an analyst who showed interest or who got excited about something the analysand was saying would be guilty of incomplete transit through the oedipal phase of his or her own transference neurosis, etc. Therefore, we were all taught by clinicians who had been taught by relatively emotionless supervisors and lecturers.
This happened to fit perfectly into another error of the analytic system: Even though Freud said that the reason the analyst was to remain emotionally non-communicative was that this increased the "anxiety" in the analysand and therefore increased the flow of "material" from the unconscious, we now know that shame is the specific negative affect triggered when someone does not respond to our questions or react to what we have said. Without knowing it, the analysts were triggering shame every time they used their technique. Can't blame them, because genius has to start somewhere, and it really doesn't matter if the first try contains an error when it produces so much good results. Unfortunately, the use of a shame-inducing technique made it impossible for shame-based people to get help for their problems, which is one of the understandable reasons that trauma and abuse patients did not come to clinical attention until the mass of therapists abandoned the "still face" style of being a therapist.
Now our problems often hover about the other locus---too many therapists have forgotten that it is our responsibility to remain centered rather than go off as if we were part of the patient's problem. It is always important for us to be disciplined, to balance between normal reactivity (central to empathy) and professional skill (which allows us to center ourselves after experiencing what has overwhelmed the other person.)
So of course I agree with you that it is unacceptable for the contemporary therapist to be nonreactive, but both of us know that the other extreme is counterproductive for reasons that become increasingly important as we deal with more and more people who have been terribly abused.
When will this job get easy?