While that would reduce violent crime, it would also sanction people using recreational drugs besides alcohol, tobacco, and caffeine. Many voters and politicians find it against their religious or moral beliefs to allow other people to do recreational drugs besides the ones they themselves are doing.
Arguably it would take time for the violent crime to subside. A culture of violence does not vanish over night, but rather over generations.
My prediction is Mexico's violent crime spilling over to the US resulting in a drug war surge (both already happening to some degree.) In the background, regulators slowly loosen up laws as to not lose face (would explain the toleration of medical marijuana.)
I can only imagine that from the outside American appear completely crazy. Regulators and lobbyists write the laws, bankers and the wealthy fund the enforcement, and then both parties consume them in obscene quantities. The exporting country pays the price in blood and corruption. From my perspective as an American, that's not crazy, that's evil.
Homicide and other violent crime rates tracked pretty tightly to the creation (and eventual repeal) of alcohol prohibition laws in the US. Homicide rates dropped dramatically immediately after prohibitions repeal. We likely wouldn't need to wait "generations" to see a benefit.
One of the articles points is that violence is used because there are no other means to settle disputes. In a legal atmosphere, the legal system could be used instead of violence.
In additional, legalization would cause prices to crash because the risk would drop significantly. Even so, in a legal environment there would still be a black market because regulations would still impose restrictions, but it would be more like teenagers paying homeless guys to buy beer and cigarettes.
