Separating "weed" [sic] from "drugs" is like separating beer from hard liquor; it's all the same, some is just a little more potent. While there's no doubt that alcohol has a detrimental effect on many, the key difference between alcohol and narcotics is: VERY few alcoholics resort to robbery or violence to get their next drink. If you think that Cannabis doesn't cause ruined lives and death you may want to familiarize yourself a little better with just how much of it people like Pablo Escobar are responsible for producing. While I can't say from first-hand knowledge, rumour on the street is, he may have hurt one or two people...
The main issue with the legalization of cannibis however is that there is NO accurate roadside tests for it. There are a number of tests in use, but they are at best only about 60% accurate, which means that drug addicts can be as high as kites, get into their car, and cause an accident with relative impunity.