How do we know there is a causal relation, @Mark Vink ? This is the difficult bit.
Yes I realise on the one hand that this is the difficult bit, just like with any other treatment, but on the other hand every patient can tell you that if he goes over his limit, and that is what GET forces you to do, then you will get a relapse and the more you go over your limit the bigger the relapse and the less likely you are to recover from it.
Therefore by definition GET is harmful for this disease and CBT for this disease often contains an element of it and therefore that is harmful too