I think there is also the situation where the therapist tells the client they can say anything but not realize they cannot handle everything. So while there may be no topic that is off the table - the therapist simply does not handle some topics well. So not a universal topic that one is not to talk about in therapy, there are topics one learns to avoid with a specific therapist because of how badly the therapist handles that topic. Also, there are topics I would advise people to avoid based on the laws for mandatory reporting ( in the u.s.).