You can't compare alcohol to cannabis. The former has been deeply ingrained in society for most of human history, whereas cannabis is comparatively new and not as widespread. When something becomes that embedded banning it doesn't work. The point about rushing to make cannabis legal is that once you do so it's very difficult to turn the clock back.
Prohibition also wasn't that strict, it remained perfectly legal to drink alcohol during that period.
Hang on you're justifying alcohol being legal because it's "deeply ingrained in society"? So was beating your wife/children, slavery and paedophilia. In the civilised world none of those are legal, and I for one am thankful of it. Cannabis already has a significant place in society, whatever happens regarding the law.
Alcohol can and does kill, whether through liver cirrhosis, cancer, RTAs or Wernicke's Encephalopathy. The total cost to the UK caused by alcohol is some 21 billion, of which 3.5 billion directly out of the NHS budget.
Anyway, I find the drug classification system retarded in the UK.
Cannabis is a class B, along with Ketamine. But then good old GHB is a class C. What the fuck.