If you weren't convinced of the mass social compulsion to assign gender to things before you had children, you should certainly be aware of it after they enter your life. From the moment a pregnancy is announced, the question of whether the still-forming fetus is a girl or a boy is often foremost in people's minds.

Parents who choose to reveal the sex of their baby can be assured of a swag of gifts that accord with ideas of boyhood and girlhood. The former is dominated by khaki, navy blue and rich red, with cars, trucks and other modes of transportation often acting as motifs. The latter invites splashes of pink and purple, this time with emblems of butterflies, fairies and princesses.

Nothing influences children's education more than the behaviour of people around them. Stocksy

Before they've even arrived into the world, the rigid framework of who and what kind of person they're allowed to be is put in place – often by the people who will be closest to them.

It shouldn't be considered radical to challenge this behaviour, but deeply held ideas around a binary expression of gender are steadfastly held onto by mainstream society.

Those of us in favour of dismantling the idea of a fixed binary are accused of "social engineering", as if there's anything more skilled at engineering society than the strict policing of gender. Still, calls to "just let boys be boys and girls be girls" increase in volume whenever individuals or organisations act proactively to broaden the range of expression for both.

Yet, beyond what our own empathy even tells us, there is compelling evidence to support the idea of consciously removing gender stereotypes for our children.

Primary school students on the Isle of Wight were recently the subject of a BBC documentary exploring the benefits of making a classroom gender neutral. The class of 23 seven-year-olds spent a term in a gender neutral environment, with statements like "boys are caring" and "girls are strong" hung on the wall alongside statements affirming that all students "can be anything".

One teacher was asked to retire his use of the terms "sweet pea" for girls and "mate" for boys, and noted his own personal development following the conclusion of the experiment. That same teacher now believes "gender neutrality is something we need to look at as a country and somehow get into the curriculum".

The experiment's architect, Dr Javid Abdelmoneim, says it is about "giving children a full development so they can achieve absolutely anything they want.

"I'd challenge any sane and sensible adult to say we don't want that."

And yet there are plenty of adults who maintain a weird kind of terror around gender expression in kids. A face painter recently went viral with a thread on Twitter as she outlined what she saw as a contributing cause of male violence in America. She recounted an interaction with a four-year-old boy who had asked for a butterfly to be painted on his face. His mother denied his request, insisting instead that he get something "for boys". The mother then turned to the boy's father, "a big guy in a jersey", and had him confirm that he didn't want his son having a butterfly on his face.

The boy's parents taught him that day to associate shame with anything considered feminine and to apply that shame to himself for wanting it. He ended up miserable, with a skull and crossbones in place of the butterfly he had wanted.

When I read stories about little boys who have their softness and love for beautiful things shamed out of them by parents ruled by their own fear, my heart breaks.

This is why it's so important to break down rigid learning around what gender is and isn't supposed to be. It's why the choice of clothing distributors (like Britain's John Lewis this week) to remove gender labels from their products is so important, and why we should also condemn the decision of schools such as Bendigo's Girton Grammar to teach their girl students how to walk in high heels to prepare them for "life after school".

Because what does it really mean, this insistence that we let "boys be boys" and "girls be girls"?

Despite what some people would have everyone believe, boys aren't genetically hardwired to like certain colours or activities. Nor are girls more inclined – as a scientific rule – to love princesses. There are almost eight billion people in the world. Taking into account the fact that some of these people identify outside the gender binary, that still leaves well over three billion girls and boys apiece. Are people really so close-minded and naive as to think six billion individuals can all be defined so easily?

What people generally mean when they spout nonsense like "let boys be boys and girls be girls" is this: "let me continue to rigidly police the gender expression of others because it satisfies my own prejudices about the world as it benefits me".

Children learn something new every day, but nothing influences their education more than the behaviour of people around them.

This is what it looks like to breed toxic masculinity. It isn't the idea that masculinity itself is inherently toxic. It's that masculinity is so fragile it needs to be protected by shrouding it in shame and fear and aggression. And as the face painter put it, a little boy learns this lesson every time "he is not allowed to love something as miraculous and beautiful as a butterfly".

Yes, let's let boys be boys and girls be girls. But let's let each of them decide exactly what that means for them. What are we so afraid of?