Some great points, Reine. I mentioned earlier that my intent in engaging in these discussions is never to undermine diagnostic systems that offer real help to humans who are suffering. In this case my point of view is from the perspective of someone studying how systems of classification have historically been used both to help people and to control them. (Big fan of Michel Foucault)
Yes the phrase "old guard" is definitely a generalization. (This is just an online forum after all!) In this discussion I would say the pharmaceutical industry is one example of a group that benefits from being able to influence diagnostic criteria. For serious mental illness medications are life saving and necessary. For some of the less serious diagnostic criteria, it could be argued that medications are overly prescribed.
Another example can be seen in how the mental health industry has changed the definition of hysteria to "conversion disorder", in order to do away with the negative connotations associated with "hysteria". I have read about instances in which the label "hysteria" was applied to women, not to help them, but to "keep them in their place."
There are countless other examples of how labels can be used to help but also to control.