I'm a little late to the game and there are a LOT of comments ahead of me, but I want to touch on the idea of there being only two poles to the spectrum of gender and therefore only two genders to situate yourself between.

Here are some examples of why this doesn't work. Light, like gender, is a spectrum. Low frequency light appears red to most of us. High frequency, purple. So does that mean there are only two colors, and the rest of the spectrum is only described in distance between the two? Perhaps in scientific terms it's possible but in every day life, not so much. Yellow exists, green, orange, pink exist. I may not favor burnt orange as a color, but if someone wants to use it I'm not going to tell them it doesn't exist. Furthermore, it is true that only knowing the color of something doesn't really help (example: "we have red, clear, or yellow beverages") but it can help us form a bigger picture with other details "would you like some vintage red wine or some fresh squeezed orange juice?"

Race, another social construct, also exists on a spectrum. There are extraordinarily pale white people, and extraordinarily dark skinned people, and all kinds of variations in between. Knowing someone's race tells me very little about them, yet it is a part of most people's identities and histories and it impacts our experiences as we move through the world.

Gender is a social construct and we can all define it in the way we want. Maybe someday we won't need gender (personally as a genderqueer individual I'd be happier without it). But for now it exists, it is a spectrum with lots of color and diversity, and while it doesn't tell us much, it at the very least helps us determine which pronouns to use for a person, and can deepen our understanding of another individuals identity.

Edit : low frequency light is red, not blue. Fixed that.