Are you referring to calling a trans person by their biological sex?
When a stranger is yelling at a trans person about their biological sex, it's done to inflict emotional harm on the trans person. They transitioned away from that gender to reduce harm (that is the definition of a trans person), and the stranger is intentionally trying to bring that harm back.
Imagine shouting at a woman about her "biological breast size" because she is wearing a push-up bra, or had surgery to enlarge or reduce her breast size. Would that seem like a normal, harm-free way to interact with another person you don't know? Obviously not.
> Who is saying that people should be harmed?
The rights actions speak so loud no one can hear their words.
https://www.nytimes.com/2022/05/17/briefing/right-wing-mass-...
https://www.businessinsider.com/right-wing-extremists-kill-3...
https://www.salon.com/2021/06/25/filling-the-trump-void-righ...
See? :)