The overwhelming problem that Argentina faces related to drugs is the level to which the corruption reached into the government, police, etc. As a libertarian, I think it's incredibly stupid to have a prohibition on anything considering that humans will find a way to get what they want; but governments don't worry about human motivation, they worry about enforcing what those in power think is "right" with little or no motivation factors considered. If it wasn't like that, I wouldn't be worried about governments to begin with.
If we have to have government, though, I can understand at least clearing the corruption of the drug trafficking out of the government and securing the borders against open planes flying into the country to deliver drugs for transshipment to other countries at the very least.
And for a country that is in prohibition, Argentina is pretty liberal with marijuana use:
Por decisión de la Corte Suprema], la tenencia de marihuana para consumo personal ya no será penalizada en Argentina. El máximo tribunal del país resolvió que la posesión de pequeñas cantidades de cannabis, que sean para uso individual y no representen riesgos para terceros, no tendrá carácter de delito.
Para fundamentar la decisión, los magistrados entendieron que este tipo de tenencia queda en la órbita de la intimidad del individuo, respaldada por el artículo 19 de la Constitución (”Las acciones privadas de los hombres que de ningún modo ofendan al orden y a la moral pública, ni perjudiquen a un tercero, están sólo reservadas a Dios, y exentas de la autoridad de los magistrados”), y como tal no puede ser castigada.
So there is indeed, as someone above mentioned, a difference between prohibition and illegal narco trade. I think Macri is trying to get rid of the influence and corruption of the drug cartels, not enter into prohibition itself. If he is trying to enforce a prohibition, well, he can't according to legal precedent and I would be very much against that as well.
Prohibiting the use of marijuana is as stupid as prohibiting the use of alcohol, considering it is actually less harmful than alcohol (we use alcohol to kill biotic elements for crissake! I have a friend who had cancer and swears that taking marijuana oil helped cure him when the doctors couldn't get rid of it!).
As to what governments should do about drugs: People will find a way to do what they want to do. Prohibiting the use of any drug is tyranny against the individual unless that individual's direct actions are affecting third parties. Let people do what they want until they hurt someone else with their actions, and then act on that. Governments cannot legislate happiness and they shouldn't be able to force others to be happy either. It's up to individuals and their families and friends to deal with unhappiness and the desire to escape from reality and no government program is going to alleviate such feelings. In fact, I'd say the worst entity to turn to in order to resolve any personal problem via "programs" would be just about any government.
But again, allowing corruption and influence from anyone or any organization into the government itself, is something that should be stopped as completely as possible if we are going to have governments.