But how will this make things better?
In many ways. In addition to the ways I already explained above, there would be no drug war constantly pumping up the police to ever greater levels of power to disregard our fundamental rights. This will save tremendously on the cost of police forces, as well, since drugs being legal will also suddenly be cheap, thus no need for the commission of crimes to support habits, and no gang wars over drugs, since drugs would no longer be particularly profitable in the underground economy.
But what I am interested in is the negative externalities associated with increased drug use. Without question, drug use will skyrocket. How is that a "solution"?
I agree with Bill Buckley on this question, viz., "I came to the conclusion that the so-called war against drugs was not working, that it would not work absent a change in the structure of the civil rights to which we are accustomed and to which we cling as a valuable part of our patrimony. And that therefore if that war against drugs is not working, we should look into what effects the war has, a canvass of the casualties consequent on its failure to work."
"I have not spoken of the cost to our society of the astonishing legal weapons available now to policemen and prosecutors; of the penalty of forfeiture of one's home and property for violation of laws which, though designed to advance the war against drugs, could legally be used -- I am told by learned counsel -- as penalties for the neglect of one's pets. I leave it at this, that it is outrageous to live in a society whose laws tolerate sending young people to life in prison because they grew, or distributed, a dozen ounces of marijuana. I would hope that the good offices of your vital profession would mobilize at least to protest such excesses of wartime zeal, the legal equivalent of a My Lai massacre. And perhaps proceed to recommend the legalization of the sale of most drugs, except to minors."
) I notice that Sri Lanka and other such counties have very little problem with drugs. 
