This is particularly harsh on women who need female-only spaces away from any males.

For example, prisons are sex-segregated to prevent male predation on women. In some places, because of 'trans rights' activism, the authorities have incarcerated men who call themselves women in the female prison estate, and some of these men have sexually assaulted, raped and even impregnated women prisoners who were trapped there with them.

So you will find a lot of radical feminists and gender-critical feminists disagreeing with this slogan on that basis. And many other people too, when they learn about how women are being harmed by this.