The belief that drug abusers will harm others physically or emotionally and steal to get their fix is true but it is greatly to deal with the drug war that is causing those extremes just as it caused the beer drinkers to turn into just that during prohibition.
The result of it being better if they legalized just pot isn't hard to say, it is a foregone conclusion at this point. Just doing that would decimate the cartels as that is the lions share of their markets while also allowing the government to regulate it for quality and ensure it isn't laced with anything before sold and would keep billions in the US every year rather than having it siphoned off in the black market funding that crap bringing in mountains of tax revenue and keeping cops from chasing them to pad their resume anymore and once the "Bad" factor has worn off, the actual rate of younger kids using actually goes down from what has been shown when similar has been done both here and around the world. With the added benefit that once pot was legal, even the local crime goes down from people trying to rob dealers or rob for dealers and such because Walmart doesn't accept payment in stolen DvDs nor do they try and push other drugs on you while you are there.