Campaigners for laws requiring people to use the facilities of their “real” gender, and the laws that come from such campaigns, often make reference to the sex listed on a person’s birth certificate. As if the information on it is somehow a sign of what should be forever.
Here is a specimen UK birth certificate in the 2013 format:
Note the space for father’s occupation. If we are to bar people from using facilities which do not match the sex listed on their birth certificate, then natural justice requires we also bar their fathers from changing jobs or ceasing work.
I understand that some jurisdictions list weight on birth certificates. Let us push as hard for laws against people being a different weight from that listed as we do for laws against changing gender.