I hadn't even seen this thread until today, so I feel a bit like I'm arriving at the party at midnight (although I suppose that feeling depends upon the sort of parties you go to).
Mentalism is a subset of magic, just as, say, property law is a subset of law. There are materials that are of interest to commercial property lawyers that are just too specialised to matter to general lawyers, sometimes even ones that dabble in property law (doing a bit of conveyancing, in among the discrimination claims, sale of goods actions, cowboy builders, divorce and will-writing).
With magic techniques, there is also the fact that secrecy is important. While we are largely willing to share some secrets and ideas with other performers, there are some things that only people with sufficient experience 'should' see, and yet more that perhaps we only share with our friends, with certain particularly hot concepts kept back for ourselves.
By creating a mentalists only section, it can encourage people not only to post ideas that fall into the second category I listed above, but also to get an idea of who might fall into the penultimate one.
I wouldn't have a problem with being excluded from an escapology section, for example. As it is, I've still not been allowed into the Naked Mentalism area!
I think part of the problem is that Craig uses the term 'magician' in a perjorative way. I am sure that he has a lot of respect for a lot of magicians, but the problem he's getting at is (at least) two-fold.
The first is a lack of respect for a branch of magic that almost requires subtlety. Many mentalism effects 'look' easy, certainly compared to those expensive boxes on stage, or years spent learning a flawless backpalm, or to do 20 straight Faro shuffles while balancing a pen on your nose.
Those who've not taken the time to study the field
might think that all there is to a book test is saying the word. That doesn't apply to all magicians, as experienced ones should understand the real work, but there are plenty of performers who just want to do cool stuff that gets great reactions. Even long-time magicians can miss exactly why an effect is powerful. Getting a good response (when they should be getting a great one) may provide false validation.
I think backs are put up because Craig tends to express this as being of universal application to magicians, when really it's a generalisation and perhaps one that's not too generous to magicians.
The second issue is to do with approaching mentalism like a magician. I think there is more than one aspect to this. The first is 'thinking like a magician' and covering all possibilities, instead of having the right 'mental' (:wink:) attitude. I don't think this is relevant to the current discussion.
The next element is the generalist approach of some performers. I think the clearest illustration of this is the story Craig has of a clown doing the MOAB at a child's birthday party. It's a great book test, but I doubt many people would justify its inclusion in a kids' show. Clearly, to Mr Blinky (or whatever) it was a great trick, so why not fit it in alongside the magic van, and balloon animals?
However, this point goes further. If you do kids' shows, or restaurant work, does your persona support you doing a 'proper' mentalism act at all, even if kept separate?
Does your credibility suffer if someone remembers you with the big wooden rabbits at their Katie's ninth birthday bash while you are on stage acting like an expert in psychology, or someone who has the gift of precognition?
What about the credibility of another performer who has dedicated himself to mind reading? Do you care? Should you?
There is some validity in keeping mentalism apart from other types of magic. When Derren Brown started doing his 'mind control' work, he specifically distanced himself from card tricks and other magic. That wasn't entirely successful, because some people rightly spotted that he was still doing tricks, but I see why he did it.
On the other hand, Kreskin used to do magic tricks on talk shows, but always made out that this was just a hobby, and unrelated to his actual work.
This doesn't mean you can't study, or like, other types of magic; it's often invaluable, as it allows for cross-pollination of ideas.
It is certainly possible to work more than one style of magic, including mentalism. What I think bears some thought is how we, as performers, can give ourselves and our audiences the best possible acts.
Sorry for the huge post, and for veering off-topic a bit. I am trying to explain why a separate mentalism section is justified (it's buried in there somewhere!)