Rachel Dolezal, and the difference between being transgender and transracial

So in the wake of the Rachel Dolezal kerfuffle, there has been a certain amount of talk about "well, if we accept that transgender people are the gender/sex they say they are, why don't we accept that people can be 'transracial' or 'transethnic'"?  And although my gut feel is that they are very different phenomena, when I started writing this post, I had no way of articulating why.  I think I now have a better sense of that, but would welcome other viewpoints.

I'm exploring half-formed thoughts here, and apologise in advance if any of it is offensive, but will of course do my best not to be.

In some ways it would be easy to just say, well gender and race are different, so analogising between the two is never useful, but I think that's an over-simplification. They are different, but they are also both ways in which our society gets divided up, they are both complicated mixtures of physical, biological and social aspects, and they are both axes of oppression. 

I think that perhaps part of the difference is that sex is roughly diamorphic, and you can fairly easily divide humans into "people who can get pregnant", "people who can impregnate", and the group of "fuzzy edge cases who are neither or very rarely both" is small enough that it just gets brushed aside, or split between the main groups depending on obvious physical characteristics, and on a first reading, the people who impregnate (or who look like them) end up with structural power over the people who can get pregnant (or who look like them).

Whereas race is much fuzzier - there are lots of them, and although white people of West European descent tend to sit at the top, there's a whole network of structural power imbalances, and there have always been mixed-race people and varying degrees of passing, and races which are viewed as white in some times and cultures but not others, and the questions of to what extent white-passing mixed-race people, or people from a culture/ethnicity which was once viewed as non-white but now isn't have a right to claim non-white identities have been ongoing for years. 

Jumping a bit here...  There are lot of different trans narratives.  Some trans people knew they'd been assigned the wrong sex when they were toddlers; some always knew something was wrong but couldn't put a finger on it until they encountered other trans people and it all clicked, some never even realised anything was wrong for years, but then life seemed much easier after transitioning, and some people have fluid gender identies which change over time, either gradually over the years, or constantly and frequently. There are trans people who have excruiating dysphoria over a body which is the wrong shape, and there are those who only have dysphoria because of the assumptions people make about their gender because of their body, and there are those who have no dysphoria at all.  And we* accept those narratives as all being valid without asking any of the people who espouse them to articulate to us what exactly it is that gender means to them and why they can't just live as a feminine man or a masculine woman. 

We've established that the traditional view of sex is pretty diamorphic, and that gender identities and performances are very tied up in that binary - people distinguish between male and female(bodies) and masculine and feminine(psychologies), and butch and femme(presentations), but even in doing so they nod to the assumption that male/masculine/butch and female/feminine/femme go together.  So it makes sense that people who don't fit that assumption deal with it in different ways, and that those ways are affected by the way society treats people based on how it genders their bodies, psychologies and presentations. 

I think I might be getting closer here to why race doesn't work like that.  My feeling is that racial identity is mostly a combination of culture and the way society treats you; it is, if you like, intrinsicly more extrinsic than gender.  That whilst there are raging stereotypes about what people of different races are like, even most people who hold them conciously would attribute a lot more of them to upbringing and culture than to a direct effect of genetics.

In fact, yes, I think I have convinced myself.  I think that the way gender ties into what is a mostly dimorphic sex categorisation meanst that being transgender makes sense even when you strip away the patriarchy, whereas race is fluid and mutable enough that when you get rid of white supremacy it pretty much just disappears, and so tranracialism stops making any sense at all.

*using the royal we here a bit, but certainly most of the people I know who are of a liberal a pro-social justice inclination