The debate about the social acceptability of alcohol over cannabis is a slurred, slightly incoherent one that has been going on for years. Each substance inflicts its own damage on the user. But what about those of us who use neither very much? Which do we prefer? After all, a city centre could never be over-run by doped-up students; they'd be in their rooms, being somnolent and boring. They might be developing psychotic illnesses, but at least they aren't peeing on our walls.