The argument about there being a small number of transgender individuals in the military can be reversed. As I see it, people are claiming that there aren't that many to begin with, so why are we worrying about them being kept out?
But it could just as easily read: there aren't that many of them to begin with, so why are we worrying about them being allowed to stay?
If they're such a small percentage, then I doubt we're going to see upsurges in unpreparedness, unit decohesion, etc.
But that shouldn't be the argument for allowing them to join the military if they want. That's just a comment on what I see as the weakness of the counterargument.
Being black isn't a mental health status.
It used to be, albeit before we had fancier phrases like "mental health status."
Michel Foucault writes of madness in the eighteenth and nineteenth centuries that stories or analogies of humans acting like animals were
no longer an indication of the power of the devil, nor a result of a diabolical alchemy of unreason. The animal in man was no longer an indicator of a beyond, but had become in itself his madness, with no reference to anything other than itself, his madness in a natural state. The animality that raged in madness dispossessed man of his humanity, not so that he might fall prey to other powers, but rather to fix him at the zero degree of his own nature. Madness, in its ultimate form, was for the classical age a direct relation between man and his animality [...]
Now bear in mind that in the eighteenth and nineteenth centuries, blacks were considered to be more primitive, closer to their natural, or animal, state than whites were. They exhibited a closer proximity to a "wilderness existence," according to eighteenth-century naturalists. Concomitant with that understanding is a classification of blacks as cognitively inferior, as having minds more like animals than humans--in other words, they were, by nature, insane. Coincidentally, this also became one justification for colonialism, since those of inferior minds needed to be helped. The rise of modern institutionalization is not a continuation of this practice, but it is historically parallel.
The recognition of transgender people within our society is still new, and until we've dedicated more efforts to perceiving them and treating them normally, we need to take any proposed study with a grain of salt; because while those studies will reveal quantitative information about transgender health, they will also silently reflect the conditions that give rise to that information.