There are millions of regular pot smokers in America and millions more infrequent smokers. Smoking pot clearly has far fewer dangerous and hazardous effects on society than legal drugs such as alcohol.
If the cost of retailing and distribution is the same as for legal tobacco cigarettes, about 10¢ a gram, then selling the (legal) product at exactly the same price as on the street today ($10 per gram) could raise $40 billion to $100 billion in new revenue. Not chump change. Government would simply be transferring revenue from organized crime to the public purse.