Predictably, these kinds of comments have provoked all kinds of (mostly affected) outrage about the violation of liberal discourse rules. The grievance, as I understand it, is that it plays on various forms of bigotry to suggest that mental illness is playing a role in our politics. So for example, when Frost calls PUMAs histrionic, she isn't simply incorrect: she's allegedly endorsing and wielding an oppressive sexist stereotype about women being afflicted with hysteria.
Undoubtedly this indictment seems uncontroversial to certain varieties of leftists, and there are some good reasons for that. But it's worth noting that, both historically and theoretically, the taboo against a role for mental illness in political criticism is hardly universal, and is actually directly at odds with another prominent and powerful tradition of leftist thought.
The Foucauldian and Frankfurt tendencies
Perhaps the best way to understand the conflict here is by identifying two opposing tendencies.
The first I'll call "Foucauldian", since it's most famously exemplified by the work of Michel Foucault - particularly in Madness and Civilization. There, Foucault argues (among other things) that mental illness is socially constructed, and that it is therefore an instrument of power and oppression. This perspective became most influential in the second half of the twentieth century; its stronghold has always been in academia, but on occasion it has had significant impacts on medical practice and public policy, for instance in the Hearing Voices Movement, which advocated the depathologization of schizophrenia. Today, this perspective is largely expressed on the left in protest against ableism, as we see in the criticism of Frost.
Against all of this, however, there is what I'll call the "Frankfurt" tendency, since it's most directly and exhaustively demonstrated in the work and theory of the Frankfurt School philosophers. Largely inspired by Marx and Freud, who sought to understand human affairs from a strictly scientific perspective, the Frankfurt School (mostly) described mental illness as an empirical phenomena. They also differ from the Foucauldian tendency in understanding mental illness as not only an instrument of oppression, but as a cause of oppression. Thus, for example, writers such as Adorno and Fromm developed sophisticated theories about the psychological basis of phenomenon like fascism and the so-called authoritarian personality (theories that may have some relevance today).
Today, the Frankfurt tendency's empirical conception of mental illness has almost entirely triumphed over the Foucauldian tendency's social constructionism. we generally accept, for example, that schizophrenia is a disease of the brain, even though we do not yet have a clear understanding of the neurological specifics. Similarly, even though the left now understands hysteria as a social construction, we primarily think of it that way because it was proven to have no scientific basis. Now the medical perspective usually takes precedence, and speculation about the social construction of mental illness is only admissible once we agree that there's no scientific basis for it. Chomsky, in his discussion of theories of psychology, makes these priorities quite clear:
What is the scientific status of the claims? What social or ideological needs do they serve? The questions are logically independent, but the second type of question naturally comes to the fore as scientfic pretensions are undermined.Again, this likely has the ring of common sense to the modern reader, but only decades ago leftists would have been far more skeptical about Chomsky's "scientific" claims, and would have begun first by investigating mental illness's social construction. As Foucault himself put it, what defines mental illness
is the action that divides madness [from non-madness], and not the science elaborated once this division is made...we must speak of these actions re-examined in history...Certainly the left indulges in episodic bouts of skepticism about the social construction of mental illness; we are for instance always guaranteed at least a handful of radical thinkpieces within the Foucauldian tendency every time a new edition of the DSM makes the news. But these are exceptions.
The contradiction of "mental illness"
And yet, the Frankfurt tendency's victory has not been complete, either. For while we largely accept mental illness as a scientific rather than an ideological term, the left remains distinctly ambivalent about its role in political oppression. Sundry grad students and writers like George Lakoff will occasionally venture theories about (for example) differences between the Democratic and Republican brain; but for the most part, the left still meets talk about mental illness with decidedly Foucauldian suspicion.
As mentioned, this usually takes the form of allegations of ableism. Critics who recognize in bourgeois or reactionary behavior the symptoms of mental illness are typically accused of demeaning it, or othering it, or in some other way oppressing it, particularly if the diagnosis comes at the expense of another aspiring leftist.
This, I think, is the central contradiction of the modern left-discourse on mental illness. There is, as the Foucauldian tendency (I think rightly) points out, an inescapable normative judgment being made as soon as one identifies a certain ordering of the brain as a dis-order; but instead of owning this judgment, and accepting the necessary implications about deviance, we reflexively disown it at the point of etiological analysis. Indeed, this move is absolutely necessary if we are to then understand the mentally ill as victims of a disease - who should be protected from potential ableism - rather than as victims of a socially constructed label - and who are thus already victims of ableism by the very at of diagnosis. So the way that the left talks about mental illness today may very well be expedient, but it is not all that coherent.