The idea of biological gender itself is a stereotype that reinforces gender binaries and gender norms. This idea suggests that there are only two distinct biological sexes, male and female, and that these sexes are directly correlated with specific gender roles and behaviours. This in turn reinforces prejudice against those that do not conform to the pre-assigned identity of their birth sex.
Gender is not simply a matter of biology, but is shaped by societal norms, and power structures. The prefix “Cis” means “on the side of” and in the case of gender means that an individual’s gender identity matches the sex they are assigned at birth.
TERFs leverage upon the cisgender construct and utilise their existing rights to block the rights of Transgender people and view trans women, not as women, but as biological men — and therefore consider them members of the ruling patriarchal class. So even if a biological male chooses to live as a woman and adopt a correspondingly subordinate social position, TERFs believe trans women will never be able to truly experience being a woman.
Transpeople have the right to exist and to live their best lives. Their choice is what they choose to do, and if they are causing no harm then it shouldn’t bother you.