Conservative logic: Punish those who misuse guns, but don't mess with the liberties of the law abiding.
Liberal logic: Guns are the problem. Ban 'em, and to hell with individual liberty
Liberal logic is to ban weed because of the relative few who would abuse it. I say let adults make their own decisions, and punish only those who misuse marijuana.
My objections to recreational weed are simple.
There is no established 'norm' by which to measure intoxication quantitatively. (BAC .08% with alcohol)
There is not relatively fast test by which such blood intoxicant levels can be measured, and no way to determine driver levels of impairment objectively, aside from behavioural observations.
Unlike alcohol, very little active ingredient regulated supply exists, and predicting the effect of any given dose is simply not possible, nor the exact effect of that dose, even on the same individual.
Alcoholic beverages have a single active ingredient, Marijuana has more than one, complicating the above.
So determining who is actively misusing the substance is sometimes problematical, especially in the case of 'edibles'.
Despite understanding the effects of and regulating against the use of alcohol and motor vehicles, the problem persists, with lethal results. A disincentive to operating a vehicle under the influence of pot is the additional charge(s) possible from the drug itself. Simply enough, let's not unleash another (legal) intoxicant on the highways.
People exercise incredibly poor judgement under the influence of either, one is enough.
There is an experiment in play, where (iirc) all drugs were decriminalized in state law, let's see how that plays out.
(Besides, stoned people are more easily manipulated). (Soma, for those who read Brave New World).