Legalize weed and half the crime due to drugs will end almost over night so to speak. But the funding for a lost war will drop and the government will look like fools.
You can legalise weed properly or legalise weed improperly.
Lets first look at legalising weed properly...
On large scale production, this stuff grows fast and can pump out huge amounts per hectare. You can tax it a little bit but also ensure quality and prices are better than street prices. Because late scale production is possible with high return, most of the cost would probably be in packaging. Through this method; the street market will quickly be squashed out.
It may further cut the usage of other hard drugs as most people are exposed to such through the underground drug culture that they may obtain their weed from.
The ability for residents to own up to one plant each for personal use would be the most ideal.
So, how would we go about this improperly?
Well through taxing it and setting prices higher than the street price as well as quality of product. This keeps up the demand for a cheaper and overall higher quality product. In turn, keeping the underground illegal trade going and the crime that goes with it.