Are you arguing that your self-identity should be defined by whether other people accept it? Or agree with it?
If you want other people to accept or agree with your self-identity, this necessarily means they will have input into the definition of that identity. We're not talking about how you identify yourself to yourself. We're talking about how you identify yourself to others, and what they should do with that information (if anything).
Or that your self-identity and where you feel you belong doesn't matter?
It matters, but it is not the sole or overriding factor in all cases.
Why should any one not feel like they belong anywhere they want or in any group they want or not in others that they don't want?
It depends on the feelings. Opinions are one thing. Feelings that are not consistent with reality are something else - usually a problem that needs to be solved, not a personal reality that should be catered to.
Put aside the complex subject of trans issues.
Heh.
I am Scottish. I identify as Scottish. if there is a special activity going on for Scottish people I would feel like I belong in that group.
I am also British. I don't identify as British. I don't feel British. If there is a special activity going on for British people I don't feel like I belong in that group.
Other people could feel the opposite, or feel they belong in both. None of it would be changed by what the other people in those groups felt about me.
It depends on the special activity, and whether the people organizing it intend it to be exclusive.
If the activity is voting in in Scottish elections, your belonging to the Scottish group has very little to do with your feelings, and very much to do with whether other people actually recognize you as Scottish.
If the people running the Australian government think you're Australian, you not feeling Australian won't exempt you from their sanctions on not voting in Australian elections. Self-identity only goes so far - only as far as the end of your nose, in fact. Beyond that, how other people identify you is going to be a big factor in determining how you interact with society, and how society interacts with you.
I'm struggling to see what it is that you aren't getting to be honest.
Clearly.
What I'm not getting is any attempt to answer this question: To what extent is trans-identity a matter of doing whatever you want based on how you perceive yourself, versus doing whatever society allows you to do based on how society perceives you?
Put it another way: Why does Boudicca, a transwoman, believe she doesn't belong in male spaces?