That means it will take time. Not that it will never happen. The evidences grow that tobacco, alcohol and krokodil is bad for the health, and that cannabis is on the contrary one of the most efficacious and safe medication. Humans are not that stupid, but the bandits have good propaganda methods.Cigarette and alcohol companies will lobby against it because it'll take a large portion of their market share. Growers and dealers will vote against it because it'll put them out of jobs. The government won't allow it because its too difficult to collect taxes on it and because of the lost revenue from taxing the piss out of alcohol and cigarettes. I would however vote for free unlimited Krokodil for any adult willing to sign a waiver for it.
Things progress: decriminalization of all drugs in many countries, and legalization of cannabis in two US states, and one country Uruguay. Prohibition will stop for the same reason that prohibition of alcohol will stop: even the bandits can't afford it in the long run. Lies cost exponentially. Prohibition injures people exponentially.