Winning Position: Yes, it should.
This is an issue of some importance to me. I am pro-legalisation, and I shall hereby make my case.
1) Soceital beneifts.
In the Netherlands (Amsterdam being the crux of this point), Marijuana is legal for use in public coffee shops and can be bought in small quantities.
http://en.wikipedia.org/wiki/Drug_policy_of_the_Netherlands
This approach leads to reduced crime rates in the country, some of the lowest in Europe, and that's across all crimes. It is shown here that while Marijuana may not be responsible for this respectable society, it cannot be said that its use will increase crime rates. This completely refutes that argument.
I have included the Netherlands' drug policy because it is arguably the best, and so I would propose that we at least base the laws on theirs, but if you would like to make adjustments, feel free.
2) "The war on drugs".
Even those who would say that it is a very harmful drug should see that by legalisation, its use would likely decrease per head capita. Nothing spurs the use of a substance more than prohibition, as can be shown by the United States' prohibition of alcohol. So if you want to reduce the total consumption figure, legalisation is the best option to achieve that.
Secondly, legalisation would destroy the illegal trade of Cannabis. If corporations were permitted to produce it, the price of Cannabis would plummet, and it would not be nearly viable for organised crime gangs to traffic drugs, as people would rather buy it safely on the high street (no pun intended) and for a price far lower than any dealer could make a profit on. Drug cartels simply would not be a viable enterprise, and many in existence would crumble or have to change to other drugs avenues, reducing the scope of policing and making those other drugs easier to combat. This not only removes the massive cost of policing the underground drug trade, it could bring in tax revenue, should the drug be taxed.
Please do not post any arguments based solely on conjecture, evidence should be used, unless you simply want to state an opinion - don't expect the line "Drugs are bad, I know someone whose life was ruined because..." to be taken seriously.