Frankenstein monster is kinda like Trans folks or people

[Sheldon]

The objective evidence conclusively demonstrates that human identity is more complex than the set of chromosomes that you're born with.

Until such time as we have objective evidence for what gender a person is, we will believe their subjective testimony without objective evidence. 

There is a clear diagnosis for gender dysphoria included in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), a manual published by the American Psychiatric Association.

So it's not a purely subjective claim, anymore than someone claiming to be gay is a purely subjective claim, it can be objectively tested, and homosexuality was also classified as a mental disorder until fairly recently, hopefully this will change for gender dysphoria as well, but its existence is objectively evidenced.