The imminent legalization of cannabis in Canada is prompting all kinds of anxiety. Will it make it even harder for teenagers’ brains to develop? Will stoned drivers slow traffic to a crawl? Will your plane’s pilot be higher than the aircraft? These may be the least of our worries. The bigger social menace of legal dope is that it will make more of us even dumber and more self-absorbed than we already are. Culturally speaking, writes Peter Stockland, the party’s about to get a lot duller.