after all, I involuntarily gender every single person that I meet in my everyday life, I put all of them in neat little male/female/no idea boxes in my brain yet I never see their genitalia or their chromosomes

The other problem is that "male" and "female" don't exist in nature.

They're words we make up. They're words that describe trends. They're not realities.

Some species have "two" sexes and high sexual dimorphism. Other species have two sexes and extremely low sexual dimorphism. Some exist in in-between states or even states where a creature swaps sexes within its lifecycle.

Male and female are just words we invented that then we attached meaning to. They aren't absolutes - nature doesn't deal in absolutes, it deals in gradients. There are gradients of everything.

Two is less complicated than three, and so the reason most sexual species of animals present with two "sexes" is because it is less complicated and it is sufficient to produce the genetic variation in a population for that population to survive.

There is no reason under other circumstances it couldn't be three. There's no reason at all for it to present the way it does, and nothing wrong with fluidity iinside of that.

The single greatest thing that I see from the scientifically ignorant is a lack of an ability to understand that the words we use to symbolize things are just that - symbols. Approximations. They aren't the thing. There's no true male and true female. There are people with Y chromosomes, who generally present with a penis and testes. There are people with no Y chromosome, who generally present with a vagina.

They're trends. Commonalities. DNA is mutable, prone to error and mutation and that is the driving force behind evolution. We're always producing new things, but these people can't fathom that. Their thinking is too rigid, too reductive, too simplistic, and so they want just two boxes and they want everything to fit in those boxes and then they tend to react violently to anything which does not fit in those two boxes.

There is no "gravity" - there's a pattern of observed phenomena that we have given a name, but the universe doesn't bend to our taxonomy. It's the other way around. We must bend to nature because words are abstracts, and nature is.

And there's a lot of not-super-bright people out there who continually and perpetually fail to understand the difference.