For arguments in support of legalization, duck into the friendly shop and offices of the BC Marijuana Party, in a small pocket of the city sometimes called 'Vansterdam.' With books, hemp clothing and associated paraphernalia, this is the place to make some new, like-minded buddies during your visit. Also, nip next door to the New Amsterdam Cafe, a popular herbal smoking room.
You'll likely smell the aroma of 'naughty cigarettes' on streets around Vancouver: it's still illegal here, but the police don't generally bother with small-scale home users. You'll also likely notice many 'pot shops' throughout the region; Vancouver is currently going through a process to issue business licenses to establishments that sell medical marijuana, so long as they meet certain conditions.