The most effective argument is that it is a "Gateway Drug". There is no proof that weed makes people use crack or heroin but it is a good way to scare the public.
Marijuana is a gateway drug to other illegal drugs because it itself is illegal. In order to get marijuana you need to go see a guy that is ALSO selling other drugs (the kind that are actually dangerous).
Legal marijuana makes it so that people don't start using more dangerous drugs on a whim. They are no longer presented with an easy opportunity.
If pot is on the same level as alcohol which do you think is more of a gateway drug? One that makes you introverted and cautious or one that makes you more confident while simultaneously impairing your judgement?
It's also a 'gateway drug' in that you don't go crazy and commit mass-murder when you try it the first time, so you start to disbelieve all of the anti-drug propaganda and maybe decide that 'they' were lying about the harder drugs too.
Legal marijuana makes it so that people don't start using more dangerous drugs on a whim. They are no longer presented with an easy opportunity.
If pot is on the same level as alcohol which do you think is more of a gateway drug? One that makes you introverted and cautious or one that makes you more confident while simultaneously impairing your judgement?