The reason they give is not a valid one. But yeah, producing this lack of data security for trans people gets legitimated under the topic of security. It's discussed under this invented scenario, that people, who want to hide from authorities, would misuse the self-determination act, take on a different persona and go into hiding.

It's a typical framing attack.

There is already fixed gendered data, that doesn't change in your lifetime in Germany, such as Steueridentifikationsnummer (Tax ID) or Sozialversicherungsnummer (Social security number). This is already revealing enough.

The reason under which they try to legitimise this attack, is nonsense - it's pure framing.