>>40826633 (OP)
It's on a basis of equality.
Cis people are often able to receive treatments to align their gender identity with their appearance. If a guy has medically significant gyno he can get a breast reduction. If a cis woman has a masectomy from cancer treatment insurance covers her getting breast implants.
If cis people are able to receive care like that for causes beyond their control...Why not trans people? Because we're "healthy"? The line blurs there because very often trans people do have observed abnormalities that back up dysphoria as a treatable physical illness. See the ongoing research Dr. Powers is making into figuring out why so many trans people share very similar comorbities in rates that absolutely scream correlation to a physical cause.
Being trans is a physical, and mental illness that is treatable through surgeries and medications that cis people already receive through insurance. Even genital surgery is allowed for cis men and women by insurance when necessary for their wellbeing. We don't just nullify guys who get their dicks blown off by bombs we construct a penis for them because it gives them better mental outcomes. But they could totally live "healthy" nullified.
We just want equal care.