Denies them access to the identity they feel is their true self
Do we all get to "access" the identities that we feel are our true selves? I think we do not. That is not some sort of right.
We do not, for example, confirm to people with anorexia that they are fat and need to lose more weight. We do NOT confirm people's dangerous fantasies.
Some people are trans women and some are trans men. We should help them live their best lives. But we must do this without supporting misogynistic and/or homophobic solutions.
Ok, so you think gender is fluid. Now let's consider kids going thru puberty. Puberty is very uncomfortable for almost all kids. Couple that with the fact that at this age cognitive development is incomplete, social pressures are high, and logical thinking is impaired by raging hormones.
Given all of this, you think that kids with GD
know for sure that they are in the wrong body that we should allow doctors to perform irreversible, dangerous, interventions - and now add on to that your belief that they might well just change their mind because (you think), gender is fluid?
Great! Then we're fine, and nobody needs to have their genitals publicly inspected or hand in a genetic test to prove who they are
Have you heard of "self-id"? This horrible idea seems to be sweeping across Europe, it will probably come to the US all too soon. The idea is that a person can self-identify as whatever sex they choose, change their minds as often as they want to, and no other action is necessary. One result of this is that criminal men who have been convicted and are about to be sentenced declare themselves to be women. So they are put in women's prisons where they go on rape sprees. Similar things happen in shelters and restrooms and locker rooms. This puts ALL WOMEN at heightened risk of assault and rape. ALL WOMEN.
This is a thorny problem to be sure. But we need to find solutions that help trans people live good lives, without putting ALL WOMEN at risk.