I am not against any human being living his or her life in the way that they want to, once they do not injure or infringe on the rights of others.
I am against the concept and belief system of 'Gender Identity' replacing the material reality of 'Sex' as the differentiating characteristics between girls and boys, women and men.
'Gender Identity' is, at best, a wholly subjective internal feeling, impossible to prove or legislate for. At worst, it is a reification of outdated and oppressive stereotypes, a means by which to equate being of a particular sex with having a particular type of personality: if your personality (or 'Gender identity') doesn't match your genitals, you must have been 'assigned' the wrong sex at birth.
Sex is just a fact, and the physical differences between the sexes - and/or male exploitation of those differences - are the reason why we need women's sports, separate spaces for personal care, women-only refuges, separate prisons, and protections in law to prevent discrimination on the basis of sex.
Replace sex with gender identity in any of those contexts, and you are undoing the work of feminism, not furthering it. Because in ideological terms, much the work of feminism has been to resist and subvert the notion that our personalities -
our interests, behaviors, aptitudes and potential - are determined by our sex. And in practical terms, much of the work of feminism has been about creating and protecting safe spaces and equal opportunity for girls and women in sport, in the workplace, and in politics.
So an ideology that says it's your personality that determines your sex, and your male size, strength and socialization should not prevent you from racing against the girls or working in the women's refuge, is not an ideology that's consistent with feminism.
Discussing the implications of this discourse and seeking to prevent changes to the law that would roll back sex-based protections isn't about being against anyone. Framing it that way is just a handy tool for silencing women.