I think this is often an emotive debate as people on both sides have opinions, justified or not, about marijuana. Therefore I have tried to keep this to a brief summary of the facts for and against:
It's not that bad.
-Generally not very physically harmful, especially compared to widely used legal drugs.
-Thousands of years of use mean that a good amount of empirical evidence has been gathered as to the effects.
-Near impossible to OD on.
-Numerous medical applications from pain relief (almost unique in that it doesn't cause "pain return" or a tolerance to build to the effects) to anti-emetic, anti-spasmodic and relief from asthma and glaucoma.
-Unlikely to cause violent behaviour with the exception of exacerbating existing mental health problems.
-By-products (seeds and fibres) can be used for paper, clothing, food, fuel etc.
-Many artists and thinkers credit marijuana with unlocking their creativity or thought processes. As well as all the musicians, special mention should be made to Carl Sagan, as well as martial artists Bruce Jun Fan Lee and Eddie Bravo, both of whom invented new ways to practice martial arts and are on record praising marijuana's effect of increasing blood flow to the brain.
It's not that great.
-Smoking anything is not great for your lungs.
-Pot will not magically make you an intelligent or creative person if you are not already.
-If you think you're deep & mystical when stoned, try recording your ramblings on tape or in writing and re-examining when sober again. Good chance you were just talking shite.
-Super Skunk is not the same as the natural varieties grown and there is evidence that the chemical balance present may cause or exacerbate existing mental illness in predisposed individuals, as well as having disastrous effects on developing brains with persistent heavy use.
In conclusion:
It should be a personal choice for adults to make. Either decriminalisation (allowing possession and light cultivation) or full legalisation for adult use would be the most sensible policies.
-Nothing one does should put them at risk of incarceration if they harm no-one else. One's possible ill health does not justify the pretty much inevitable ill-effects of putting non-violent drug offenders in prison with rapists and murderers.
-Tax revenue from legal marijuana sale could put many crisis-ridden economies back in the black.
-Regulation would allow for quality control and monitoring of the level of consumption by individuals, enabling problem users to be identified early.
-Enormous profits which currently fund criminal organisations would go to legitimate businesses, tax collectors, or in the case of decriminalisation, simply find their way back into the economy through legal means.