It won't be and it shouldn't. If people enjoy it fair play to them. If it harms no-one else then why ban it. Drugs are banned yet still widely used.
As Lee said, it does harm other people. Try telling the late Roy Castle's relatives that smoking doesn't harm other people. The poor guy never smoked, buy died from Lung Cancer caused by passive smoking, during years of working in the clubs.
Smoking Cannabis , has the potential to harm other people, because a lot of 'users' will drive while under the influence of the drug, knowing that the Breathalyser can't detect it.
Drug users can, and do harm other people, as they will steal to feed their habit. They also leave their Hepatitis and HIV infected syringes laying around, where children could pick them up.
A "healthy smoker"?, I don't think so. They may be physically fit and playing sports, but that doesn't mean that damage hasn't, and isn't still being done to their lungs and cardio vascular system.
Maybe not be evident to them now, but it is there all the same, and the 'debt' may well be collected later in life. As I said earlier, its a game of Russian Roulette.
Dave