But that's the point isn't it? The reason why pot is illegal is that we don't have an effective way of preventing people from getting high (or even reliably testing for intoxication) and driving/operating dangerous equipment/etc., and the potential for people getting killed is reason enough for the law to intervene.
Laws will never cause everyone to make the right choice, but they do cause most of the people to make the right choice. Legalizing every behaviour may allow us to say there are no criminals, but it would make living in our society worse for everyone, and that's why we have laws and prisons.
No, read the history; we made pot illegal in 1923 because darkies used it for fun, and you know what their kinda fun was. Before that it was a legitimate over the counter medicine; you could Google Asthmador™ as one of the medicines, and look up Emily Murphy's*
The Black Candle for the racist sensationalism.
The huge number of lawbreakers incarcerated in the US for minor drug offences should have put the lie to the naïve belief that laws make us behave, I don't know why you're repeating that cant. Laws tell people what their lawmakers have decided is the standard for ordinary behaviour. When the people disagree with their lawmakers — as with drugs (most spectacularly during Prohibition), gambling and sex — all the laws in the world don't stop them.
I don't know what you're trying to say when you talk about legalizing every behaviour, as that has nothing to do with anything said here. We have prisons to lock up bad people. When we define common, ordinary behaviors as cause for imprisonment, we run out of jails — as they have in the US — and have to make room by releasing 'criminals' — as they have in the US — with no way of distinguishing the real baddies, from the ones our bad laws created.
But I agree that "we don't have an effective way of preventing people from getting high …", nor to prevent them getting drunk, or taking too much Nyquil™, but we do have laws against dangerous impairment in general, and driving while impaired in particular. Those laws have failed to stop drunks from driving, so it's hard to see how they'll do any better with any other drug. But we will have them to use against the bad people who only exercise judgement after they've impaired it. A few years of low-cost MADD campaigns have done more to make people decide not to drink and drive than all the millions we've spent on roadside checks and legally invulnerable Breathalysers.
But if you really think making drugs illegal keeps our roads safe, why isn't alcohol illegal? It's far and away the most abused drug, and the one involved in the most crimes on and off the road.
Anyway, fascinating as this is, it's far off topic, and I think you haven't made a general case for prohibition that could apply to tobacco.
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* Murphy's well worth a Google, not everything she did was as blinkered and hysterical as her pot crusade, and she well deserved her picture on our $50 bills as one of the Famous Five.