My point was that if prop 19 had passed, then if after a few years bad thi8ngs didn't happen as a result of it, then that fact would change the tone of the debate on cannabis legalisation, leading to a big majority being in favour of people being in favour of it. When that happened, it'd be time to tweak the law to change some of the bad parts of it (because no law is perfect).
Why would someone vote for a law that seemed to them likely to create harmful side effects rather than waiting for a less ambitious, better-designed law that wouldn't? That's the conundrum I think many people fell into. You can say "the perfect is the enemy of the good", but that ignores the fact that the bad is also the enemy of the good.
> Why would someone vote for a law that seemed to them likely to create harmful side effects
Because as well as the bad effects, the law might also have good effects, i.e. be a net improvement. Most policy proposals have some potential bad side effects -- if they didn't, people would already be doing them.
So if a policy appears to be net-positive, it is probably worth supporting.
> rather than waiting for a less ambitious, better-designed law that wouldn't?
If a referendum fails, it may make it less likely that a better designed law will come along later. This is IMO the case for the referendum on electoral reform that will be held in the UK next May -- see http://en.wikipedia.org/wiki/United_Kingdom_Alternative_Vote...
