A brushback pitch works because the batter's subconscious screams "it's gonna hit you!" The body reacts to a close call almost the same as to actual damage, dumping adrenaline and intensifying senses, increasing heart rate and respiration. It doesn't matter that your conscious mind is telling you "they want to scare you, not actually harm you."
This is what microaggressions are like, except that they're usually accidents. Someone thinks it's funny that a man wore a dress -- they're not attacking, but they find gender-non-conforming behavior to be so alien that it is funny and you know from long experience that if someone can't relate, they can be cruel. So a giggle becomes a near blow. Or someone uses a slur to describe an upsetting situation -- they're not attacking, but they're showing a lack of understanding that also allows for cruelty. So a bit of slang becomes a near blow. It doesn't have to be physical to cause intense physical reactions which use up your physical and mental reserve energy.
I used to be such a bold and brave person, back when being myself didn't cause constant flinching. Back before I knew [TW: general mention of violence against oppressed people]how many people get fired and beaten and raped and murdered for varying from the accepted norm, not to mention being ostracized and excluded by default. Before I knew the consequences and before I knew myself to be at risk, I was free. I was just a little bit different and people thought it was quirky and interesting, not threatening and overwhelming. It's easy and safe to be yourself when who you are does not disrupt people's belief systems.
Now my system is so exhausted from the constant jolts of adrenaline I endure in day-to-day interactions with people that being myself becomes almost impossible. My body doesn't even wait for people to say stuff anymore. It just dumps adrenaline as soon as I'm doing something that exposes me to people, no matter how small and innocuous. When it's about to be my turn to talk in front of people, my body is acting like I'm about to jump out of a plane. I'm not afraid in my conscious mind but my subconscious doesn't care. I'm not shy, reserved, or introverted, but I have become anxious and on the outside that looks the same. I have become literally unable to be myself thanks to an endless series of brushback pitches.
But after many years of having no financial safety, I finally have a job where I can take care of myself. I can afford to offend biofamily. And after many years of feeling unnourished and unvalued, I have people in my life who really do love me as I am and value what I offer. I can afford to lose friends. I still get thrown brushback pitches constantly, but I'm wearing some body armor now, and I don't flinch quite so hard. I plan to make armor for others, as well as dismantling the system that creates these pitchers who give us nothing but brushback pitches.