Well, like I said, why make something that is harmful legal? If you're only argument is that something else that's just as harmful is legal. That won't fly.
And there is no way to tax pot. It can be grown anywhere, by anybody.
And there would be "garden patches" in everybody's back yard. Making alcohol in your basement is illegal. Growing pot in your backyard would then be illegal? Haven't solved the problem of prison overcrowding then.
How do they tax tobacco? How do they tax legal moonshine? How do they alcohol?
You tax pot the same way. If you want to grow it then you have to get a license, you want to sell it you get another license, you want to possess it then you get another license. You could even go so far as to have different classes inside those three examples. If you get caught with it and you have no license then you go to jail or a ticket depending.
The US has spent billions of dollars trying to prevent people from smoking pot. When they could be making billions of dollars. Do you think that if there was a license offered to you for say $100 a year and you possess up to 5 joints at a time, that people would not pay it? Liquor licenses for food places can be as high as $45000 in some locations and that is just to sell liquor and not beer, that would be another license. You could make these fees as high as you want or what the market would bare.
They can tax anything they want to. The reason they dont is because a lot of people would be out of jobs and the kick back money would stop rolling in.
My brother works as a TFO for the DEA. When they do these bust for pot (mostly from the Mexicans) His department gets a portion of the money that they seize and property. He brings in millions of dollars a year for his department.
Some say that is a good thing but the reality is that his department can not use that money for operating cost (paying deputies, vehicles, etc). So it doesnt help the budget at all.
His department just spent $100,000 on new firearms that they didnt need and they are currently sitting at the department. The money came from drug bust and they were going to lose it and the feds were going to get it.