The engineering mindset is to have it support both use models, but that is explicitly what people don’t want. Hidden features which enable authorities to enforce toxic concepts.
What toxic concepts can authorities enforce with your birthDate that they could not already enforce with your realName?
This is a question that nobody has an answer to.
The entire premise of this argument is that adding birthDate allows for some new kind of oppression not previously possible and so it should be fought or else someone will use it in a bad way.
Except, if that were true, these hypothetical evil forces could already have access to your REALNAME and LOCATION. Both of which are fields that have existed since the 60s.
That hasn't happened, those fields, like birthDate were added to allow support for some use cases and outside of those uses cases (which, you have to choose to implement because you are in complete control over your system in the FOSS world) the fields are completely optional and not used.