One question just how are they supposed to get the money to pay the fine if they are jobless and homeless?
You can't be fined if you have no money. If you're arrested, they must supply you with a warm place to sleep and food. Where's the down side?
City and county jails are not the Dickensian nightmares that state and federal prisons are. They usually don't have enough individual cells so the hobos and winos who are there for a day are two are not locked up with just one cellmate. Most of the people are there for similar offenses, primarily drunkenness but a few small-time hoodlums, so there aren't a lot of violent people there. Of course bad things do happen in local jails, but the odds against it happening to you are high.
I've seen women fall asleep while sunbathing. If I were homeless and saw that she wasn't fined/arrested, I'd be suing for discrimination.
I might get stabbed by a jealous hobo after I fell asleep on a bench, call the police and be taken to jail for telling him how I got stabbed.