I see The Big Problem as:  Ok...let's say it is 'legalized' for use in public (even if it is in a "Lounge"), may we safely assume No One who will smoke in public will NOT be driving themselves home afterward? 
Yesterday I saw a van from CA with some young "hippie-wanna-be's", and as the side door opened a cloud of Cannabis assaulted the nostrils of anyone nearby. I suspect they were here for the Country Fair bacchanalia. I care not if they smoke - But I DO Care a lot that they then would be Driving!