As I understand it, you sort of get to choose your gender, but society has to accept your choice.
If I declare myself a woman but make no attempt to "live as a woman" as society sees it, I'll appear to be taking advantage of the system, and my choice will be rejected and there will be social consequences.
Conversely, if I do appear to be making an honest attempt to be a woman, and you don't accept it because of your conservative values, then you cannot reject my choice, because that's bigoted.
Yes, you can change your mind about your gender, but you really need to do it in a life-upending way that feels risky and permanent and committed, then you'll be celebrated. If you phone it in, people are going to be offended and you'll be rejected.
It would be both sexist and transphobic to expect trans-women to "appear to be making an honest attempt to be a woman" by conforming to some outdated view of womanhood.
Cis-women can do anything (including any traditionally male activity like date other women, wear jeans, like football and monster trucks, like anime and video games, and in some cases, even grow beards) so why can't trans-women?
https://en.wikipedia.org/wiki/J._K._Rowling#Name
As I mention in my other comments on this thread, it's not right to judge people on why they identify with a particular gender. Whether it's economically motivated or not, if you accept that people can choose their own gender, the reason for the choice doesn't matter.
I think that is exactly not how it is supposed to work.
Do you believe this to be ethical? Because to me I find it rather offensive considering it harms actual transgender candidates.
Well, the answer is that people that are transgender will have a history of being transgender or acting in such a way that confirms they consider themselves that gender. So any lawsuit as a result of this would look into your past, see that you lied about being transgender and make it an open and shut case. If that case became public then you could say goodbye to your job prospects.