Read everything Julia Serano has ever written 😆

EDIT:

1. parents’ rights

Anti-trans legislation removes parental rights - it takes away the right of a parent of trans children to give them gender-affirming care. Checkout this interview with the Arkansas Attorney General about making gender affirming care for minors illegal - this doesn't support parental rights, it strips rights from parents. See around 2:25 mark, she mentions it's just about getting a second opinion, Jon Stewart points out the state law doesn't let you choose, you are forced to not get treatment under criminal penalty.

2. “What is a Woman?”

Ask them if they think the definition "adult human female" is any better, since it essentially just claims gender = sex, a woman has to be female, etc.

If they go for that definition, then show them countless examples of women who are not strictly 100% female, e.g. ask if they saw Alisha Weigel in public, would they think that is a woman? She has XY chromosomes and is a male with complete androgen insensitivity syndrome. She looks and lives as a woman, but isn't an "adult human female" - this definition fails in lots of cases, this is just a great one to get the intuition pump going.

If they just think that Alisha Weigel is "technically" not a woman because she's not "technically" a female, remind them that nobody knows anyone else's chromosomes when we call them a woman, nor usually their genitals, nor loads of other information about their biology ... and yet we somehow manage to squeeze people into one of two boxes labeled "man" and "woman" anyway - and Alisha Weigel was easily put in that woman box, and if they're arguing she should be in the "man" box instead, ask whether she should use the men's restroom, whether she should be treated as a man when considering her risk for breast cancer and so on ...

Hopefully this kind of reasoning re-establishes that actually our notion of being a woman is the common sense one, and that the anti-trans definition of a woman requires we violate our eyes and intuition.

3. your brain isn’t fully developed until you’re 25 [bad science btw.]

Explain that most people have a sense of their gender at an early age, that we don't question a cis person's sense of their gender at a young age just because their brain isn't fully developed, and that most trans people have some knowledge that their gender is wrong from a young age even if they don't know how to interpret their experience and don't realize this means they are trans.

Furthermore, gender identity doesn't change, it seems to form during fetal development, and if someone has a persistent sense of their gender younger than 25 (which all of us do), then there is not much reason scientifically and medically to question that. Finally, we don't require cis people to wait until 25 to decide they are men or women, what justifies having a special rule for trans people?

There is a cost to forcing trans people to go through the wrong puberty and to wait for crucial gender affirming care, not allowing them to take puberty blockers because they aren't 25 is insane, it shows a disregard for their life and a willingness to allow a lifetime of suffering and increased likelihood of suicide simply because ... what, trans identities are suspicious to cis people? This isn't controversial in the medical and scientific community, why do you think you know better than nearly every association of scientists and doctors?

4. “why is there a whole pride month?”

Why is there a Black History Month? Besides, why does this matter, pride month doesn't hurt anyone and it implies homophobia - ask why it matters and see if they can articulate what is wrong with it, I guess.

5. trans regret

Regret rates are extremely low: https://whatweknow.inequality.cornell.edu/topics/lgbt-equality/what-does-the-scholarly-research-say-about-the-well-being-of-transgender-people/

Regrets following gender transition are extremely rare and have become even rarer as both surgical techniques and social support have improved. Pooling data from numerous studies demonstrates a regret rate ranging from .3 percent to 3.8 percent. Regrets are most likely to result from a lack of social support after transition or poor surgical outcomes using older techniques.