Correlation is not the same as causation. It's a logical fallacy. Caution is always a good idea, but the conditions of a practice don't determine the ethics of the practitioner. As has been said, the nature of therapy is private, whether conducted in a solitary setting or a shared setting. There are factors that can be looked at as indicative of an ethical practice, but being in sole or group practice probably reflects economic reality more than ethics.

I experienced my T in both settings; while I responded differently, he remained the same.