But they won't.
Agreed. Though a big obstacle to the idea of “writing off the Ts” is that a small subset of the people who identify with the transgender group really are anatomically and/or chromosomally intersex due to biological circumstances beyond their control. These people can make a pretty airtight case in a court for being allowed to choose to live as whichever gender they choose. And it’s a slippery slope from there, when the next layer wants the same right — and by the next layer, I mean the ones who may very well have some genetic or developmental abnormality that isn’t detectable by current medical science, but which may very well become detectable in the foreseable future.
While I estimate that 3/4ths or more of the people currently calling themselves transgender are just muddle-headed attention/sympathy-seekers, who ought to be written off without hesitation (with the write-off effecting a miraculous “cure” in the great majority of cases), the presence of the other categories precludes a simple solution to the whole issue.