A person's **sex** is how you know who has what and who to mate with. A person's **gender** is an arbitrary social construct. It is a set of stereotypes of how males and females "should" act, dress, what they should like/dislike, etc.

Well what is gender. Is it a reflection of a persons biological sex or a masculinity/femininity spectrum? If it's a spectrum then how many genders are there? Everyone falls on different areas of that spectrum. There are plenty of cis women who are more masculine than the average man. There are also plently of cis men who are more feminine than your average woman. Do we have different gender identites for every person? At that point gender becomes obsolete. Do we break down the spectrum into different sections? Well that what if someone identifying as a cis man falls more on the feminine side than a demi-girl (or whatever a semi-feminine man is called). Is the cis man wrong about who he is? Either gender correlates with sex or gender is obsolete.

Whether you support trans people or not is irrelevant. If gender and sex mean exactly the same thing, then we're just gonna need to invent a new word to describe what we mean when we refer to "gender". Seeing as language evolves over time, adding nuance between the words "sex" versus "gender" is just useful. The most important thing is that everyone understands what everyone else is saying. Differentiating sex and gender helps us do this better.

To argue that an interpretation of gender, distinct from sex, holds any significance is to argue the validity of gender stereotypes. Just freaking live your life the way you want to. But realize you don't have the right to dictate how everyone else has to interact with you.