“I don’t understand what is so upsetting about being deadnamed”
Names are power. Names either give power or take it away. Think about a parent giving a child a religious name to try to presuppose a religious identity at birth, and the USSR renamed cities after Lenin and Stalin to deify them. Naming is an act done by the powerful to the powerless to reinforce structures of power.
As such, the renaming practices we undergo when our egg inevitably cracks, whether we pick one name or cycle through many, we take power for ourselves. To choose a name for ourselves is to take power away from those who maintain the power structure, whether it be the government or religion or what have you. And that’s also why the oppressive structures seek to deny the personhood of the oppressed via deadnaming.
Choosing a name is in fact that deep. I recommend reading Thomas J. Gasque’s “The Power Of Naming”
https://www.divorceny.com/wp-content/uploads/sites/177/unsorted/Files/harrington-lecture-Gasque%5B1%5D.pdf
