Although he says to "beware" of those psychologists who are "too identified" with a particular kind of intervention, clients may be looking for a particular brand. But what Dr. Shedler is aiming to highlight with his emphasis on "too," is that as clinicians we have a responsibility not to impose our "brand" on our clients. We have an ethical and clinical responsibility to intervene in a way that meets their needs and/or be able to recognise when we cannot and make the appropriate referrals.
While it may be true that you will find therapists who have done work in a lot of areas, it is important to recognise that some areas are connected and may overlap, while some may be so far from each other that you may have to honor some skepticism you have about the depth of expertise purported by the the clinician.
Additionally, emphasis on diagnoses can be both positive and negative. Most clinicians try to work with specific populations. Old or young, trauma or depression, posttraumatic stress or bipolar disorder are ways in which we can "funnel" our expertise. It is hard enough for clients to choose a therapist and these buzzwords can help guide client choices. However, it can also be an anchor that holds all parties involved, below the water.
Either way, there are many things to consider and these are just a few of the ones that needed some extra attention. Feel free to read Dr. Shelder's article and leave comments below.