I don't even need my therapist to be GC, I just need them to respect the fact that I am.
I've had perfectly good, mutually respectful, helpful therapy from a practitioner who profoundly disagreed with me on trans issues — I even told her that though I understood that she was in no way intending to advocate for dangerous treatment, unlike her I believed affirmative therapy for young people with gender dysphoria was at best poor practice and at worst a form of abuse which could lead to profound harm, that treatment leading to the sterilisation of disproportionately gay and autistic young people was highly suspect, and that if she were to perform that type of therapy, in my opinion she would be, however inadvertently, potentially abusing and harming vulnerable people.
And you know what, it was absolutely fine. The therapist didn't try to educate me, or gaslight me, or turn me into someone else's support droid. We explored my thoughts and feelings about this topic, why it bothers me, and how that ties into my life, my politics, my sexuality, my autism, etc. etc. — y'know, therapy stuff.
I wasn't made to feel my beliefs and feelings were wrong just because they were different from the therapist's, or less important than the beliefs and feelings of genderists. Who knows, maybe she secretly judged the hell out of me but it doesn't matter because (a) that didn't show in session, and (b) the therapist didn't then publish an article in an industry magazine revealing dismissive and patronising attitudes towards my opinions and feelings. (They do know clients can access these things nowadays, right?)
The issue isn't so much having a therapist who disagrees with me, it's having a therapist who doesn't behave like a fucking therapist — where, if I'm the client, I'm the client, and what matters is what's best for me. Okay, relationships are part of that, and if one of the things I'm taking to therapy is that I want a better relationship with my gender-dysphoric kid, then discussing whether it's worth making concessions and changes is going to be part of that, but I don't expect the therapist to decide they know what beliefs I should change and what outcomes I should value, what fucking TV programmes I should watch, and what my function as a parent is, and therapise me with a goal of their choosing.