I think I've come up with a metaphor that clarifies my view of gender.
Imagine a big table with tons of dishes laid out. Some of them are physical traits, some of them are psychological. There's everything here from "big biceps" to "played with dolls as a child." And there are all traits here, not just things you'd associate with gender--this is a table of traits, not of mixed up boy things and girl things. "Brown hair" and "likes classical music" are on there too.
Go ahead, load up your plate. Load it with anything.
And the really important thing here is that the dishes are not paired off. "Chest hair" and "breasts" are not a dichotomy. You can get one, both, or neither. Ditto "watches pro wrestling" and "sews prom dresses." Certainly some dishes are popularly eaten together--"penis" and "testicles" is a perennial favorite combo, and "penis" and "likes racecars" do seem to have some mysterious association--but they're not locked together. It's possible and acceptable to have one and not the other. Then again, anything that's possible is acceptable. And any combination is possible.
Gender is a prix fixe menu. Pick one of two and eat what the chef serves you. And if what he decides to serve you is a shit sandwich, well--depending where you are and which course the shit sandwich is, the consequences range from trivial to life-threatening if you don't eat it. If you get some or most of your courses off the other menu, the fact that it's "the other menu" is something everyone's explicitly aware of.
But when you eat off the smörgåsbord, it's not really about mixing up gender any more; it's just about mixing up traits. And at that point, I feel that the entire concept of "gender," to even refer to the existence of the prix fixe menus, no longer serves any purpose. To see someone's combination of traits and go "well, yeah, but you're basically a woman then, right?" is to miss the entire point.
Ultimately, though, my cute metaphor doesn't really matter. Because whether you say "wow, it's exactly like that" or you scratch your chin and say "hmm, I see things differently," or even if you say "I'm offended by this because it seems dismissive of certain gender identity issues," you're not the intended audience. (Also if you're some sort of smartass that goes "what, 'has a gender identity' isn't a dish?") The intended audience is the people who are not reading, the people who would go "what is this gay shit" if they did read: the people who will treat people like shit if they feel they're committing a gender violation. Whether the shit consists of tiny backhands like "it's cool how you're a girl but you do guy things" or crappy pseudo-tolerances like "I don't care what you do in your private life, but you have to act like a normal person at work" or outright harassment or attack... it's shitty.
And I don't understand it. I've tried to dissect the thinking behind gender enforcement and I always get stuck. I don't think there is a thinking, at least in the sense of a set of principles that you could lay out logically and defend. I think it's more like a cognitive association. "That person looks funny" may be a shorthand for "that person is making me think too hard. I should be able to label someone in one swoop and know everything about them." There's also a heaping helping of homophobia--if someone isn't a clear gender, then maybe they can't be clearly heterosexual, and OH NO WE CAN'T HAVE THAT.
And there's just no explaining to a certain kind of person that we don't even require genetic heirs for inheritance these days, you can write your will out to pretty much who ever you want, plus most of us don't need to have more children so there will be more help on the farm, so the whole homophobia thing is seriously obselete. Go get a bug up your ass about the essential rightness and God-ordained fact of primogeniture or something.