
Yes, it is in many places. It's the sole criterion for all of Canada, many states in the US, several countries in Europe, and is on the docket for discussion in the UK.
And beyond the complete *legal* element of self-id, there's also a whole host of policies currently in place that use self-declaration as the sole criteria. For example, prison placement in California, Washington, New Jersey, and several other states, as well as participation in sports in school, accommodation in rape and domestic violence shelters, and several other venues...
like "best actress".
Seriously, in this thread, it is literally the sole criteria used in Switzerland. I mean, what other criteria do you think is in place?