There are legal reasons why you can't harass people now. The police also have no powers to simply move people on - they never did back then, but decades ago society accepted the police doing so because it generally worked. Now their "Yuman Rights" do not permit the feds to violate their freedom of movement and assembly in such a manner.
Policing worked 50 years ago because people had more respect for the police, and had some fear of the consequences, not least of which their Ma or Pa finding out. If that didn't work then everything from a clip round the ear to falling quite heavily down the stairs in the back of the police van would be deployed until the message was received and understood. Again, can't do that any more.
Until something positive is done, like putting handcuffs on them, nothing changes. Even then, once the handcuffs come off, they're back on the same bench the next day being a PITA. Having a word, even daily, even hourly, is of zero consequence to what remains of their their alcohol/cannabis/spice/insert other substance addled brains. A copper giving them a bollaricking is of no significance at all. In fact, getting nicked is often of no consequence, and is often viewed simpy as a minor and inconvenient interruption to their wastrel lives. Indeed, sometimes its welcome as the nice police doctor will give them methadone to keep them going until they can get back to the bench in the grave yard the next day.
If simply speaking firmly and persistently to people cured such behaviour we'd have been in Utopia decades ago. Unfortunately, people inclined to behave in that manner are disinclined to care very much at all about anything the Feds can lawfully do to them. All they care about is where their next can of Red Stripe/spliff/score is coming from. Getting in their faces daily - forget it. Unless you can back it up with some action nothing changes, and even then the changes are usually only very short term, and they'll be back the next day. This is why there is NO link to crime levels and police visibility.
Shoplifters don't care about CCTV. Speeders don't care about Gatsos. PITA members of the public nuisance underclass don't care about plod. Period (I hate that term, but its very apt).