Psychiatry is neither a science nor a pure science, like physics or chemistry.  The latter encompass precise, predictive laws and involve nothing outside of the realm of science.

Psychiatry encompasses approximate, predictive laws and involves subjective judgments, which are outside of the realm of science.  These subjective judgments occur in the realm of ethics (everyone is, to one degree or another, knowledgeable in the realm of ethics).

Because psychiatry encompasses ethics, it can never have the authority of science.

Now, all that being said, a part of psychiatry consists of psychiatric science.  The judgment of a few psychiatrists that Gaypracs are Gay is not a part of psychiatric science.