Having observed the effect of the smoking ban outside of the Library, I have supported enlarging the effected area. Smoking is a very strong addiction. I noticed smokers will stand in the rain to smoke, but their friends who don't smoke stay under shelter.
Smoking carries a very expensive social cost. Even people with insurance don't pay the full cost in their premium. It's subsidized by others who don't smoke. For the homeless, the cost is born by taxpayers. All one has to do is hang out with smokers like I have who in their later years are tethered to oxygen tanks to know the suffering.
So what to do about enforcement? No matter how many jails, people will get out. We need intervention programs with strict accountability. The better programs get funded. 
There will be some who never turn around. With $450 billion on military but  $50 for the entire HUD budget, is that the best use of taxes? Where is the money for the mentally ill on the streets?