Without taking positions, I can agree with you that moral relativism should definitely not be influencing such things, and yet it obviously is doing exactly that. I already saw it well enough in psychology, but you are correct that it is also becoming highly influential in psychiatry

Psychiatry has always been intrinsically political, from its earliest days in American history when runaway slaves were thought to be suffering from some kind of physiological disorder, to the present day, where modern science has failed to reliably identify particular, consistent biomedical origins of psychological distress, despite a half-century now of intense research. As I noted above, the American Psychiatric Association acknowledges this failure of scientists to produce evidence confirming the biomedical model. In a 2013 press release, Chair of the DSM-5 Task Force David Kupfer stated:

In the future, we hope to be able to identify disorders using biological and genetic markers that provide precise diagnoses that can be delivered with complete reliability and validity. Yet this promise, which we have anticipated since the 1970s, remains disappointingly distant. We’ve been telling patients for several decades that we are waiting for biomarkers. We’re still waiting. (bold added)

To this day, 7 years later, such biomarkers continue to elude researchers. Evidently, since its inception psychiatry has been a scientifically baseless ideology. Its continued prominence in society is therefore not attributable to its scientific efficacy but rather its role in establishing and regulating normative behaviors.

Again, medicine in general has pretty much always functioned as a system of social control. Over the past century, with miraculous advancements in medical science, this has increasingly become the case. As Conrad and Schneider observe in Deviance and Medicalization: From Badness to Sickness:

. . . medicine has always functioned as an agent of social control, especially in attempting to "normalize" illness and return people to their functioning capacity in society. Public health and psychiatry have long been concerned with social behavior and have functioned traditionally as agents of social control (Foucault, 1965; Rosen, 1972). What is significant, however, is the expansion of this sphere where medicine functions in a social control capacity. In the wake of a general humanitarian trend, the success and prestige of modern biomedicine, the technological growth of the 20th century, and the diminution of religion as a viable agent of social control, more and more deviant behavior has come into the province of medicine. (excerpted from Understanding Society: An Introductory Reader (Fourth Edition), p. 153, bold added)

It's true that medicine ought to be wholly apolitical. However, the reality is that, in addition to offering legitimate and effective treatments for virtually all health complications, it also has an integral role in supporting behavioral norms. The latter is especially true for psychiatry, whose treatments do not target any known pathophysiological origins of psychological disorders and whose sole function is as a mechanism for social control.

Normative behaviors generally aren't just some anomaly that came to be normative on their own. They came to be so because societies found that they seemed to work and benefit the group as a whole. They do change over time, but my point here is that people agreeing upon what is normal behavior isn't as flippant as some people believe. It tends to be time-proven behavior that generally reaps benefits for everyone.

You're painting an idealized picture of societies as cooperative, democratic, egalitarian bastions of justice. This does not at all characterize large-scale societies (or even many of their small-scale counterparts). Since the first class societies formed some 10,000 years ago, human societies have been characterized by widespread political, economic, and general social inequality. Such an environment fosters the development of oppressive cultural elements, such as ideologies, norms, and customs, that function to maintain ruling groups' power. While many social conventions (e.g., nodding for "yes," saying "thank you" after receiving a gift or being otherwise helped, language in general) are indeed harmless and have practical value, the idea that this is the default in class societies is simply untrue. Instead, such societies are rife with oppressive elements that work in service of power.

The problem with psychiatry isn't merely that it's a system of social control. All societies rely on mechanisms of social control in order to ensure members' survival, security, and social fulfillment. What makes psychiatry problematic is that, as I noted above, it is a non-democratic system of social control, as opposed to a science, whose behavioral norms are instituted by fiat. Consider that these norms reflect white, middle- and upper-class biases, which researchers have found partially accounts for the relatively high prevalence of psychotic disorder diagnoses among nonwhites and those of lower socioeconomic status (SES). Basically, individuals from these demographics are more likely to receive such diagnoses because their behavior is perceived as alien to clinicians, who themselves typically come from higher-SES backgrounds. Given that the stigma associated with "mental illness" causes those who receive psychiatric diagnoses additional distress (Corrigan & Larson, 2008) and that such people have no say in which behaviors are classified as "disordered," psychiatry does not exemplify the type of benign norms you describe above. On the contrary, this illustrates exactly the kind of cultural element I mentioned above: Psychiatry works in service of power while oppressing the powerless.

I'd say it's probably also an ideology of geographical place and shared identity that develops over time. So what?

This is corollary to the fact that it's ethnocentric. Ethnocentrism, which is defined as "the belief in the inherent superiority of one's own ethnic group or culture" and "a tendency to view alien groups or cultures from the perspective of one's own," is a myopic, unidimensional, antiscientific perspective. Again, the problem with psychiatry is specifically that it is ethnocentric as opposed to scientific, and also oppressive, not simply that it's a shared ideology.

Nevertheless, as a group of sizable proportion, I think we have a very reasonable position to demand a place for ourselves in society, but unlike the homosexuality you referenced, I wouldn't demand assimilation and reverence. I'd only demand the chance to prove my worth to your kid's future while obeying existing laws.

I don't think any particular sexual proclivities should be revered above others. Like institutionalized monogamy, this creates a sort of sexual hierarchy where normative sexualities enjoy privileged status and deviant variants face oppressive stigmatization. Instead, human sexuality in general should be respected, regardless of the particular forms it takes.

My demand is for society to eliminate the norms that prohibit adult/child sexual interactions, as these are oppressive both to children and adults alike. (For further elaboration on this point, check out this essay I wrote.) I'm not sure if my interacting with children sexually will have some kind of profoundly positive effect on their futures, but it needn't have to in order to justify these norms' elimination. Oppression is unacceptable. Period. It should not exist.

We may need a clearer definition of conservative in the sense that you intend it.

I went over this in another post, but allow me to iterate. In the broadest sense, conservatism seeks to maintain (or "conserve") the status quo, whatever it may be. Since the formation of class societies, which generated the widespread inequality I referenced above, conservatism has been characteristically anti-egalitarian—it functions to preserve the status quo vis-à-vis this inequality.

Psychiatry is conservative in both the broad and this more narrow sense. Not only does it bolster the status quo with respect to behavioral norms, but, being a biological determinist ideology, it has the effect of justifying social inequality. As Harvard evolutionary biologist RC Lewontin, Cambridge neuroscientist Steven Rose, and the late Harvard psychologist Leon Kamin remark in Not in Our Genes: Biology, Ideology, and Human Nature: "Biological determinist ideas are part of the attempt to preserve the inequalities of our society and to shape human nature in [rulers'] own image" (p. 15). Biological determinism promotes the illusion that our society's highly unequal state of affairs is "natural," immutable, and resistant to change via political means. In positing biomedical origins of psychological distress, psychiatry promulgates this illusion by diverting attention away from the deleterious sociocultural factors that are the true causes of distress, thus hindering progressive social change.

Hopefully this makes things clearer.