I don't think it is as simple a matter as saying "ok, you are legal", I would imagine the process of legalisation would bring with it many challenges - all of which I feel are worth the effort. I would support legalisation, here is why I would.

First off, the legal status of marijuana is inconsistent with the legal status of other substances such as tobacco and alcohol, two substances significantly more dangerous and harmful. Tobacco smoking is essentially a process of slow, legal poisoning and its health destroying effects are common knowledge. Alcohol not only does untold damage to the brain and internal organs, the social damage it can cause is even more severe. In the UK for instance, something like 60% of all A+E admissions are alcohol related over the weekend period, costing the NHS billions each year. The cost of policing town and city centres also runs into the millions because so many people do not drink in a responsible manner.

That it should be ok to smoke tobacco and drink alcohol, yet not smoke marijuana or take other drugs is just nonsensical, it is inconsistant and it sends out a very misleading message.

Secondly, the act of criminalisation almost certainly causes more problems than it solves. If you drive a product or service underground, where it can be afforded no legal protection, it will get into the hands of thugs. Drug dealers, not being able to use the legal system to protect their business often have to resort to violence and intimidation, drugs being one of the main sources of the UK's gun crime problem. Having the industry in the hands of thugs, with no legal duty of care to the consumer means there is no way of being sure what you buy is a quality product, there is also no way of protecting the consumer from inscrupulous dealers which in itself can lead to other criminal acts i.e., revenge attacks since there is no legal recourse.

Imprisoning people who take these drugs, and indeed in some cases people who sell them, especially when there is no evidence of violence ends up creating an unjust criminal class. People who are addicts, especially to harder drugs like heroin will not get clean if you jail them. And that someone can get a criminal record, which in itself can have a terrible impact on a persons job prospects just for getting high on an unsanctioned substance is so mind bogglingly unfair and stupid it staggers me that such a system is in place.

Thirdly, attitudes need to change. I can only speak for the UK, but there has been a massive and very successful campaign of misinformation by the state, meaning popular opinion of drugs is often very innacurate in relation to facts. It seems that drug policy is developed more with the use of muisinformed popular opinion and fear mongering than it is from facts and evidence, a classic example being a few months ago when an Oxbridge proffessor who advises the UK government on drug policy advised that esctacy be downgraded from a class A as it was no more harmful than horse riding, advice promptly ignored by the then home secratary and lampooned by certain interest groups on the media, primarily parents who lost kids to drugs.

It struck me as disgusting that an Oxbridge scientist, whose opinion is formed using evidence could be so hastily disregarded, and indeed have his opinion clouded out because it doesn't fit with popular opinion. Things need to change, I do honestly think we should strive as a society to form opinions etc using as many facts as possible, I know humans do not have a good track record with such things, but none the less it would be nice to see if we as a society could do this as it would mean we would "grow up" and stop being so childish around the drugs issue.