You haven't proposed a sensible solution.
parkrun is a charity that aims to widen access to improving physical and mental health, so please suggest something that is sensible and affordable. Unless your goal is for all parkruns to be shut down and for people to have fewer opportunities to exercise.
There are millions of parkrunners already registered, and millions more that parkrun would like to register. How do you keep participation free of barriers and also restrict it in the way you propose? Go on. What's your hassle-free solution?
I believe strongly in female rights, but that doesn't mean I have to hate trans people. Believing in female rights and trans rights are not mutually exclusive things, you know...