That’s the crux of the issue here: someone does feel the need to not fill out the field (i.e. filling it in with an “X”), and the health authority is forcing them to use either “M” or “F”. They are fighting for that right because they are intersex or trans, but an identity card with one or two fields is not the place to explain, because biology is complex. For medical information, you read their medical charts or talk to the patient.
I’m not sure you fully understand the issue. This isn’t merely about catering to a patient’s preference to be addressed in a certain way. For some, the sex / gender assigned at birth is actually wrong, and continuing to carry that information serves no purpose but to cause harm.
What is the process for assigning gender at birth anyway? People look at the baby’s genitals and make a guess. For 99% of babies, that heuristic works. But it turns out that some people are trans or intersex, and that wrong guess causes nothing but trouble.
Don’t think that the assigned gender at birth is medically useful information, either. There are dozens of intersex conditions, and crudely categorizing people into two or three bins is too simplistic.
In short, it’s complicated. The same solution is to trust that people are whatever gender they say they are, and if they need medical services, talk to them about what they need, instead of forcing them into a life course based on a genital inspection that happened years ago.
Wealth that’s just sitting there is hard to assess and therefore easy to game. What’s the value of a piece of art? It’s far more practical to tax transactions and realized gains, when money changes hands.