As crooked as the NYPD was in the 1970's, they would not turn their eye on kiddie porn or child prostitution. Millions of pole passed through 42nd street back then, it would have been shut down immediately. The news would have been all over it. Besides, how many people are sick enough for that stuff?
You're talking out both sides of your mouth here, the police were crooked enough to collude with the FBI to murder Joe Colombo but not so corrupt as to turn a blind eye to underage prostitution. Remember Jodie Foster in Taxi Driver, that was all over the city back then and while I didn't see them walking with any mobsters they were working out of venues like Sex World that were owned by Mafioso's like Roy DeMeo.
