If there was a way to tax it then it would have been done already, same with cocaine and heroin... alcohol is just as bad as the aforementioned drugs but its a taxable drug so doesnt get half the bad press it should do.
I think it should be legalised, there have been no deaths caused by marijuana yet countless through smoking and alcohol yet they remain legal. If it wasn't through taxation and income off these product they wouldn't be legal however.
They will never legalise marijuana though, would only encourage more people to grow it themselves 'legally' and selling it, causing gang fights etc etc.... would like them to look into controlling it though ala amsterdam, few coffee shops in town centres to allow it, would increase the revenue in the local high street when folk float out of the 'coffee shop' with the munchies and spend a bomb on greggs and other snacks.
Indeed there have been deaths caused directly by marijuana use - innocent people (and the users themselves) being killed by stoned drivers. Over here and in many parts of the USA the charge is "driving under the influence" be it alcohol or drugs. The only problem is proving the driver has used dope - unless it is fatal - as there is no equivalent to the breathalyser test used for alcohol, as far as I am aware. Having said that, I do agree with marijuana use for medicinal purposes in very specific and controlled circumstances - again, over here, a number of MS sufferers have campaigned successfully to use it to ease their symptoms. I don't have a problem with that.
If I was in charge, I would legalise Marijuana, Speed and Ecstasy. I would use the revenue to try and stop the use of Heroin.