I correlate being non-binary with atheism. That’s a pretty good analogy. Now supposing that all gender is a human construct, the same way all religion is a human construct, both rulesets are essentially states of non-being, a rejection of pre-established and flawed preconceptions. If someone is baptized as a Catholic at birth, for instance, then later on they can declare their severance from the Church by becoming an Atheist. In much the same way, if someone is announced a female at birth, they can declare their severance from the binary male/female model by becoming non-binary. In either case, adoption of the role requires a belief that a) Catholicism/the binary model EXISTS but is fundamentally misguided and that b) other options outside the old systems are possible. To embrace one’s gender while rejecting the concept of gender makes about as much sense as claiming to be a Pantheist and an Atheist at once. It’s a contradictory position that leads to internal conflict