identifying as non-binary is completely rational and seems to have a lot of scientific traction due to various factors such as there being more than two sexes: male, female and then a wide range of intersex conditions. society don't hear about intersex people much because they often have, so called, correction surgery at birth to get them within the sex binary; a procedure that can really mess with these kids mental health. as a society, we are so obsessed with fitting identities into binaries that sometimes fail to notice that science is backing up the non-binary argument. here's how.
so from what i've picked up most have agreed that potentially someone's gender identity and sex can not align, thus are accepting gender and sex are different. although within that they are skeptical of non-binary factors in the gender section of that equation. now if you consider that intersex conditions occur in roughly 1 in 2000 births; to put that into perspective the UNICEF estimates that an average of 353,000 babies is born every day around the world. that is about 176 babies born each day with intersex conditions. now consider that that figure only takes into account obvious intersex conditions. now apply those figures to being non-binary, because being intersex is just the more physical and obvious equivalent of being non-binary.
sex is not binary, sexuality is not binary, thus there is no real logic in insisting that gender is binary.