Crusing is not the story of Harvey Milk or some other Gay. It was originally written by a straight guy, NYT reporter Gerald Walker, who wanted to write a murder thriller based in the gay community- and it’s based on things from his point of view, and its actually spectacularly awful in understanding gays! It was probably pretty freaky for a straight person to read about bath house sex or Central Park sex in 1970 and how it got published is probably a story unto itself.
the Movie was done by straight people later, with changes- changes based on American culture. by then, people in NYC knew about gay people at least- though most Americans had never heard of S&M- which context was added to “make sense” for how a gay man could become a murderer.