Let them. It’s an empty threat.
I live in CA and I use these parks all the time (Angel Island, Mt. Diablo, Hearst Castle), especially since I have 2 boys scouts and 1 cub scout and we hike all the time, and I say. . .fine with me.
It’s immaterial to me whether these parks are National Parks or State Parks. Perhaps they’d be better off as National Parks; I don’t know. I imagine the National Parks might cost more $$ as far as entrance fees?
Not one thought of SELLING them, is there?