Even if I agree just for argument's sake that the existence of intersex people proves that some people can have "nonbinary" sexes, or "third" sexes, and that "sex is a spectrum," how does that have any relevance to people who are not intersex? Like okay, let's "agree" for the moment that intersex people are something other than male or female. How does that make YOU, as a person who is not intersex, something other than male or female? Saying that intersex people's existence somehow makes sex "complicated" for you specifically is like saying that the issue of whether or not you can hear is "complicated" because some other people who are not you suffer from hearing loss or deafness. Like sorry but for 99% of the human population it is not "more complicated" than born with perfectly normal male genitalia = male and born with perfectly normal female genitalia = female, and chances are you fall into that 99%.
Sex is not a social construct or a nebulous enigma of a concept. It is not debatable and made up in the manner that gender is. You cannot philosophize about whether there are two sexes any more than you can philosophize about whether humans have two kidneys. Someone having a missing or malformed kidney or accessory kidneys does not change the fact that humans as a species have two kidneys. Humans are gonochoric just like nearly all other animal species on Earth.
People who make this argument have never met an intersex person. They're overwhelmingly just men and women with some funky endocrine stuff happening. The odds of genital development being affected is like .0001% of the human population, and even then, it's more like 'you're not fertile' and less 'we can't tell your biological sex without genetic testing.'














