There are many reasons why feminists think that gender is harmful.
But mainly its because it underpins sexism. To the detriment of women.
Toys, clothes etc, just reinforce the idea that, for males and females, there are certain things only one can have and certain ways that only one can behave.
Making strict divisions in the societal enforced gender roles between men and women has a lot to answer for.
This is the way it was explained to me and it caused me a hell of a lightbulb moment:
When you think about the way women have been treated historically. And this is not very long ago in scheme of things.
Women were considered too feeble to vote. Literally that was the word used. It was assumed that giving the vote to women would just give two exact same votes to every household. Because they would do what their husband’s told them. Obedience.
Higher education was considered a waste of time for girls because their brains couldn’t handle it. The logic and rationality required for an education was considered beyond women. Illogical, irrational. Not enough brain capacity. And where would they find the time in between doing the housework and raising the children?
A woman wanting to leave her abusive husband was considered hysterical. And often incarcerated.
They, and their children, were considered the property of a man. If they did get divorced, the man had legal custody of the children, automatically. Without recourse for the woman.
Women are supposed to be decorative and compliant. Any objections means she must be hysterical.
Until 1992, providing sex on demand was considered a woman’s role. Rape within marriage was completely legal. And it took a whopping 15 years to get the (mostly) men in Parliament to reluctantly agree that it was wrong.
Pub landlords were within their legal right to refuse to serve a woman purely on the basis of her sex. Until the 1980s. Women drinking without a man just isn’t seemly.
Woman couldn’t get a mortgage without it being countersigned by a man. Evidently not responsible enough with money.
Women are feeble, irrational, irresponsible, illogical, unable to partake in public life because they are uneducated, as their brains can’t take it. They are there to provide sex, be seemly and obedient, keep house and raise children.
Women are oppressed on the basis of their biology.
And gender roles are the means by which it is done.