1) The accusations are based on hearsay and comments that two police officers made, which doesn't exactly constitute a force wide plan.
2) A comment I read on the internet made a very good point: vagrancy and camping is illegal in most parks in New York. When the cops are called out to move on a hobo, what are they supposed to tell him? "Sorry, only unemployed people with degrees in post-war German cinema are allowed to camp in New York City"?
I would add that this is exactly what happened with the Summer of Love. The thuggish rebels-without-a-cause (or a fucking clue) come in, sexually abusing people and acting like dicks, without any means of financially supporting themselves, and eventually the well-educated middle class liberal women get fed up and leave.