There's some context missing here, in that doubting trans people's self-identified gender is often done in conjunction with denying them healthcare they could die without. Trans people are touchy about gender for a reason, that being a great deal of oppression.
Gender and sexuality both has lots of nuances, which we could learn about from each other, in and outside of this thread. At the same time there can be hardships in such a discussion, because LGBTQ+ people face a lot of unfair treatment, and the lot of us sadly bring with us some bias from the world we were brought up in. Going into that difficult discussion, hedging on the other person lying won't lead to anything constructive. Please don't.
I honestly don't understand how denying healthcare is legal. I am very confused why stories like Robert Eads' don't end in a bunch of people going to jail. Doctors may have a right to say "I disagree that you are a wo(man)", they shouldn't have a right to deny treatment because of that.
I also understand the desire of changing LEGAL definitions of the words gender, man, woman (not that I think it is a good idea in all cases) It can also be done without changing the definition by rewriting rules and replacing relevant instances of "(wo)men" with "men and trans(wo)men"
I never said that trans people are lying, Please don't put words in my mouth. I said that people have a full right to not believe someone when they say I am X. Demanding them to accept every "I am X" claim is just plain wrong and very anti-freedom of thought. Also, I listed lying as one of the possible reasons why a claim can be false. Why are you jumping on the lying part?
*I do think that not all people who claim to be trans are actually trans, some are mistaken, especially young people but it is a rather complicated discussion. Intentionally lying and putting yourself into a marginalized group is rather... unlikely