I'm against legalising it - for no real reasons, but more the fact that I think more research into whether it actually is dangerous or not should be done first - at the moment there are very few long-term users (and studies can't dope up a group of people for a few years to carry out trials) so it cannot be established if it does cause cancer or not (it's likely to due to the level of carcinogens [ie, chemicals that cause cancer], but is not proven yet). And into whether it does affect mental health (even if it triggers people who would, for want of a better phrase, "go schizo" anyway it is still dangerous as it causes the early onset and eary destructions of someones life and social wellbeing).
One thing I do worry about is a "slippery slope". A long time ago alcohol was the only thing people needed to relax - then cigarettes and alcohol. Now people are turning to dope. What happens in a few years, or next generation, when people no longer feel dope is sufficient and, say, start taking Cocaine or Heroin en-masse. By the logic presented to legalizing Cannabis (It is going to be smoked/snorted/injected; It will be a fuck-load more dangerous without proper regulation and education [cut with rat poison/chalk]; As it stands, it funds criminal activity, or is done in unsafe environments with improper methods [dirty syringes]. Yes, these are more dangerous (in the case or Heroin) or more noticable side-effects (in the case of Cocaine), but the same logic still applies, and who knows, the social situation may have those as the commonly-taken illegal substance (with the same sort of clamour to legalisation). Such movements to legalize such strong substances would then have the "But you did it with pot!" precedent to fall back on.
Mind you, if this bill does pass and marajuana does get legalized, I can see them doing the biggest "FRAK YOU" of all - and that it would only be able to be legally purchased/smoked by California residents (for anyone else it would still be a felony; much like the pot laws in the Netherlads [or at least we were told foreigners weren't allowed to smoke it in bars but locals were, whther that's true or not I don't know]). Would mean no interstate visitors getting to get stoned legally, and the internet-rage at such an outcome would be hilariously beautiful to behold.
Neither of this affects me, being a UK citizen - and I don't smoke pot either. Honestly, I don't care if people do, and the direction the laws take it in won't phase me too much...but I hate the fact that my uni buildings keep reeking of the stuff (and it's bad enough these days when only half the people that would like to partake regularly actually have the know-how/balls to go and find a street dealer). That stuff stinks (and I prefer buzzes to 'highs' - I'm not a saint, I know from experience), makes your clothes stink (for a lot longer than cigarette smoke does too) and generally annoys me (trying to explain to a flatmate that I really *don't* want any of his bloody pizza)!