A guy has a few beers and hits a pedestrian, and the police call it the results of DUI, yet sober people hit pedestrians all the time. Low levels of alcohol do not increase your chances much of causing an accident; they do more to decrease your chances of avoiding one, i.e. reacting adequately to an unusual situation. Not that I'm advocating drinking and driving here, but saying that even 1 drink is bad is silly. Our bureau for traffic safety stated (against popular political opinion, surprisingly) that lowering the current limit of 0.05 BAC (2 drinks or so) would do very little to directly reduce the accident rates. A lower legal limit may help in an indirect way, by emphasizing the negative effects of alcohol on driving abilities, and the idea that it's easier to say no to the first drink than it is to the third. (Which is why the legal limit for young drivers was in fact lowered to 0.02).
Oddly, Magic Mushrooms are legal in Japan...but for "appreciation purposes" only. So you can buy them but you're only supposed to look at them, I suppose.