Its mental illness. Whoever has it. Females or males.
That is what until a few years ago, it was considered right along with people who deliberately amputated limbs.
It is a sub-sector of the Left that creates this cult which is advocating transgender.
Some of the support for this cult comes from older trannies themselves (the old misery loves company syndrome), some comes from the brainwashed medical field (brainwashed by the Left), some comes from parents who want to be accepted for having a special-needs (trans, in this case) child, some of it may just come from a need to belong, some comes from peer pressure.
BTW, if mental illness is defined by the distance between our perception of reality and actual reality, we are all insane to some degree. Teenages are particularly vulnernable because adapting to an ever-changing, constantly moving away "reality" is most difficult during adolescence.