My point of view is that locking people up for drug use:
* Hasn't reduced drug use
* Makes them more likely to continue their drug use
* Often leads to the use of harder drugs
* Is expensive
* Provides funding to cartels
* Causes violence
Decriminalising, or legalising drug use removes one of the main motivators of gang formation/violence while allowing the state to focus on helping addicts recover and contribute to society. The money spent on enforcement can now be spent on treatment, reducing the need for further funding rather than increasing it.
That is an option yes. It could reduce the likelihood that addicts end up in a cycle of incarceration and more extreme drug use. However, without a legal supply, I don't believe it would have any effect towards curtailing gang violence or their funding.
Personally, I believe the legal supply should be delivered by the state. With a focus on providing monitored, unadulterated doses of the safest alternative and a program aimed at weaning the user off in a sustainable manner.
my cynical take, entrenched people have something to gain by the grey area decriminalization offers.