Let us suppose that we identified all the biochemical mechanisms associated with conditions like major depressive disorder or schizophrenia. (We assume that our progress on the biological side of things will confirm those psychological categories, rather than lead to an entirely new DSM, if you will, though note that historically, we passed from terms like melancholia and dementia praecox to the hopefully more useful contemporary phrasing.) Yet would such discoveries show that these emotional and cognitive conditions must be maintained, simply because they seem to be "caused" by biological factors?
Now, it isn't likely anyway that we would find out that biology itself was so much a reliable source of the grounding you are asking about, because we would in turn have to pass from biology to chemistry to quantum physics in the one direction, and from psychology to sociology to ecology to cosmology in the other. In other words: why would biological explanations of psychology outweigh ecological ones, and so on?
Insofar as we cherish freedom of expression and yet pose to ourselves questions about "harm"-reducing limitations hereof, we face the question of paternalism. We might argue against gender-affirming care and religious enculturation on the one hand, while arguing for medication/therapy regimens on the other, vis-à-vis the various states of mind under immediate discussion here, supposing we made the relevant discoveries. However, to fully justify paternalism would require much better metaethical theories besides, much better, that is, than are currently available. Uncertainty over bridge-principles for dealing with is/ought gaps or "naturalistic fallacies" suggests that it is possible that ethical concepts are not particularly subordinate to biology, psychology, or other such disciplines (although, to be fair, it's not really known that such separations of concepts are absolute; c.f. the uptake in moral psychology as a family of research programs).
The application of dichotomies like bias/impartiality, then, must be situated to some extent less abstrusely. I.e. we can also ask about impartiality in forming theories of freedom, rather than just the impartiality (or lack thereof) of such theories "from the outside," in comparison to an external framework. And really, it would be rather incredible to think that we had to wait for decades (or centuries!) of scientific analysis of gender, religion, and mental health before coming to perfectly acceptable conclusions in practical reasoning about these topics. If our metaethics were telling us to wait on such things, it wouldn't be much of a metaethics.
EDIT: another complicating factor is the possibility that there are scientific debates that have already been resolved enough to where, if the results are applicable to some moral questions, then we're already in a position to run through those applications. For example, it seems relatively obvious to me that some people's religious beliefs were not simply transmitted to them from previous generations, and that some people's gender identities are not dependent on an inflexible biological substrate. If we make our moral theories turn on the endless progress of science, the kind of moral progress we would be looking to make could well end up paralyzing us or changing our decisions with every new, supposedly pertinent, discovery. And so I would be tempted, were I in that kind of cognitive position, to defer to whatever my local moral intuitions were telling me (if anything).