It's simple. If we legalise cannabis we will reduce crime, boost our economy as well as reducing health risks.
People will continue to smoke cannabis whether it is legal or not; once you start regulating the production and sale of this substance you will stop the money going into the hands of dealers and gangs and instead the money can be used to help "cut the deficit".
Unlike alcohol, it will not adversely lead to violence and rowdy behaviour on the streets of our cities and towns.
If it is legal, it is less likely to be a gateway drug for things like cocaine and heroine, as legitimate sellers will not be trying to make profits out of people by moving them onto harder drugs.
Once it is legal, you can make it safer for people to smoke by actually giving them a choice about what they are smoking. Instead of just buying whatever their dealer has in stock, such as high grade skunk, people can make informed decisions and know that what they are buying is actually what it says on the tin, and has not been sprayed with damaging chemicals such as raid, ether or formaldahyde.