Full Disclosure: I am one of the people helping to plan the IACFS/ME Conference.
There are two reasons why I agree with the way the call for abstracts is phrased: one is scientific and one is practical.
There is a lot to be learned from folks in other fields. For example, fatigue in breast cancer , autoimmune illnesses, and aging are thought to be mediated by cytokines to some degree. This might also be true of CFS. In breast cancer specifically, there's a lot of work right now looking at why some people remain extremely fatigued, mentally dulled, and have difficulty sleeping (i.e. symptoms similar to CFS) months, years after they have undergone appropriate treatment for their cancer and there is no longer evidence of cancer. Not too long ago, that fatigue was attributed to psychosocial reasons but new work indicates that the people post-cancer-treatment who remained fatigued in fact have genetic profiles where their genes associated with cytokines tend to be "more sensitive" and remain "on" after other people's have turned "off". (I'm simplifying here but you get the idea.) This is reminiscent of CFS. Remember the Australian Dubbo studies? They showed that the folks who were still affected after 6 months were those who monitored a more vigorous immune response initially.
So, inviting folks from other fields could lead to ideas, insights, treatments that have not been explored in CFS. In addition, this is a way to introduce them to and educate them about CFS. As you know, most clinicians/ researchers today have not been well-educated about the illness. Some researchers might even consider using CFS subjects as comparison subjects in their future studies. (One funding strategy of CFS researchers like Baraniuk has been to use CFS subjects as comparisons subjects for Gulf War Illness as GWI is better funded.) Fields like cancer and aging have a lot of research dollars, recognition, and plenty of researchers attached to them. While we work on a long-term strategy to increase CFS funding/ recognition/ etc., this is one way to move the field forward short-term.
On the practical side, if we restricted abstracts to only those involved with ME/CFS or FM and attendence to people who studied ME/CFS, we would not be able to hold a conference or survive and grow as a organization.Conferences are important; it's where scientists, researchers, and others can meet face-to-face, present cutting edge ideas, and form collaborations. Even in this age of the Internet, nothing beats in-person communication. But even stripped down conferences require money -- to pay for the conference space, the audiovisual services for the lectures, etc.
Most nonprofit scientific organizations are supported by member dues. There are simply not enough ME/CFS-focused professionals and while we can work to grown the field, there's no magic wand right now that can conjure more members instantaneously. So we work to recruit professionals from other fields that overlap with CFS in hopes they will become interested in CFS. This is good for patients too -- most CFS clinicians and researchers are aging and there aren't younger folks to take over their work.I also think the entire ME/CFS community benefits from having a strong professional organization, one that can produce a credible work like the IACFS/ME Primer written or can provide a counterweight to GET/ CBT treatment recommendations.
Another reason IACFS/ME will not "creep" too far is many of its members (yes, clinicians, researchers, board members, patients, and volunteers) have CFS, including yours truly. I would not support an organization with the limited energy I have if I did not believe that it could help me get better. I don't do things mindlessly, with no goal in mind, just for kicks.