I'm a Republican firmly in support of legalizing Mary Jane, and then taxing it to death.
One bad side effect not discussed much though is that marijuana is many times more carcinogenic than tobacco.
I had a buddy in law school who smoked weed like I then smoked my pipe and an occasional cigaret.  He died of lung cancer in his late 40s.
But the tax on it would really help the federal budget - no joking.
An interesting sidelight - the federal income tax started to rise from being just a nuisance tax to a serious tax during Prohibition, when the fedral gov't lost the liquor tax revenues.
Prior to Prohibition, the liquor tax was the main source of all federal revenue.  Come on folks - legalize and smoke your weed and drink more and maybe we can keep the Bush era tax cuts.