Leftists are happy to argue this one, actually. They consider sex and gender to be different, so a person's body can be male but their mind can be a woman's. Woman =/= female, man =/= male. Woman is gender, female is sex. Changing the sex to conform with the gender is not a contradiction for leftists, it harmonizes gender and sex.
I never understood why you need 'gender confirmation surgery' if you become a woman if you say you are.
Note the change in terminology: sex change => sex reassignment => gender confirmation.
Leftists are happy to argue this one, actually. They consider sex and gender to be different, so a person's body can be male but their mind can be a woman's. Woman =/= female, man =/= male. Woman is gender, female is sex. Changing the sex to conform with the gender is not a contradiction for leftists, it harmonizes gender and sex.