With that logic the same can be said about any mental illness

Asperger Syndrome
Autism Spectrum Disorders (ASD)
Agoraphobia
Claustrophobia
Depersonalization Disorder
Generalized Anxiety Disorder (GAD)
Obsessive-Compulsive Disorder (OCD)
Panic Disorder & Panic Attacks
Separation anxiety disorder
Social anxiety disorder / Social Phobia

etc... Maybe you just don't like the term mental illness because it has a negative connotation?

Classifying transgenderism as an illness isn't dismissive. The evidence is clear that people with dysphoria have extremely high suicide rates. 41.8 percent of respondents stated that they had attempted suicide at some point in their lives. An overwhelming majority are linked to other major mental illnesses. I personally don't think we as a society should promote a condition or mental illness (whatever you would like to call it) as something positive when clearly it creates a group of highly suicidal people.