The problem is that the people using drugs out in public are already at rock bottom: there aren't many punishments you can use to deter that, short of putting them in jail and when they come out they're just going to be using drugs in public all over again. I'm somewhat receptive to the idea of mandatory treatment but as it stands, "enforcing some harsh laws" doesn't do anything to curb recidivism – temporarily incarcerating people falling out of the bottom of society is not a long term fix for society.