It's a serious question. Hear me out please.
The Merriam Webster definition of transgender is:
of, relating to, or being a person whose gender identity differs from the sex the person had or was identified as having at birth.
It seems that being transgender hinges on the sex you're assigned at birth versus the gender identity you experience afterward. If they don't match, you're transgender; if they do match you're cisgender.
Children are typically assigned a sex at birth based solely on the appearance of their genitals. But science has concluded that a person's physical sex constitutes more than just the appearance of the genitals; the sexual differentiation of the brain is critical in establishing sexual identity. Be that as it may, children are raised as the gender that's associated with their assigned sex. If they are uncomfortable living as that gender, sooner or later they choose to transition to their preferred gender. They are by definition transgender.
But, let's consider the same child who is assigned a sex not simply on the appearance of her genitals, but on a comprehensive scan of her body and brain which reveals that she's likely to identify as female as a child. Given the results of the scan, and knowing how important it is to make the right gender assignment, her parents agree to record 'female' on her birth certificate and name her Lily. She is raised as a girl. She grows up happy as a girl except for the fact that one day, to her consternation, she discovers that her girl friends don't have penises. She accepts her parents' explanation for the anomaly and what they can do to correct it later on, and she remains a happy, well-adjusted girl.
By definition, Lily is not transgender because she's happily living as a girl; a girl with a penis, but a girl nevertheless. Still, she'd like her private parts to be like other girls, so as puberty approaches, at her request, and with confirmation from her psychologist that she's indeed a happy, well adjusted girl, her parents make arrangements with a medical team to place her on female hormones and to surgically reconstruct her genitalia to match her gender identity. It all takes place without anyone knowing about it. There's no coming out, no social transition, no controversy over bathroom use. Lily is the same girl she's always been.
One could argue she's a transsexual woman since her male genitals were converted to female, but the label doesn't quite fit either. She's not undergoing sexual reassignment because she was assigned female at birth based on the scan that showed she was born with a female brain, the most immutable sexual organ. Lily is cisgender, just as other intersex people are who are assigned the correct gender at birth despite their congenital condition.
I present this not so hypothetical thought experiment to make a point. The point is that being transgender is not an inherent attribute of a person. It is a consequence of having been assigned the wrong gender at birth. It's not as much an error of nature, as it is human error; understandable, given our limited understanding of sex and gender and lacking the technology to make better decisions, but an error nonetheless.
Many intersex children grow up perfectly happy people. Some aren't even aware of their intersexuality. Few people know that Julia Child was genetically male (XY chromosomes). She had a congenital condition CAIS (complete androgen insensitivity syndrome). She was born with female external genitalia so assigned female at birth. She was raised happily as a girl. Only her 6'-2" stature and infertility hinted at her intersex condition. Had her androgen insensitivity been partial, she might have been assigned male at birth despite having a female brain, and suffered gender dysphoria.
I contend that the official definition of intersex should include as one of its conditions, the sexual differentiation of the brain opposite the sexual differentiation of the gonads. The brain structure of males and females are demonstrably different which accounts for at least some people questioning their gender, experiencing gender dysphoria, transitioning genders, and battling the intolerance of an uninformed population.
