This is magical thinking. Organized crime can make money in other ways. This story is about kidnapping, for example. Organized crime exists in many places where it’s not funded by drug trade.
Sure they aren't going to disappear overnight. But cutting out their most profitable product lines would make a huge dent without a doubt.
We have a real-world example of that from Prohibition so it isn't entirely theoretical.
They end up extorting even more money from the local populace, and try and extend their fangs into other activities.
I’m not saying that legalizing drugs won’t help at all. But it’s unlikely it will help in places that already have gangs without other actions in addition.
Gangs exist as the most promising form of employment for people without other options. If you destroy the gang's single largest source of revenue, then it reduces their relative attracting as an employer. There are alternative to drugs like human trafficking, arms dealing and the wildlife trade but they have much much smaller markets. Perhaps in the short term violence would increase as gangs try to find a replacment for drugs, but even in the medium term I strongly believe that recruitment would plummet and attrition would rise as the money ran out.
Note that labor unions were a legitimate type of enterprise, but organized crime ran them illegitimately anyway. The willingness to break the law is their competitive advantage; it would make no sense to give it up.
It's possible the violence might actually increase, actually.
Organized crime will likely never truly go away, but it has flourished because of the war on drugs (just as it did in America during the prohibition era).
Kidnapping is more of a capital arbitrage situation. I don't think it scales like drugs. For it to be really worthwhile, it relies on people with a lot of capital coming into the area. If you scale up kidnapping, people simply don't come, or invest a lot more in security.
None of these has the absurd profit spans of drugs, though. You need about ~600-800 US$ worth of raw coca leafs to produce 1kg base cocaine (https://www.businessinsider.com/from-colombia-to-new-york-ci...) - and make ~25-27k US$ once it's on US streets. A vertical cartel that controls everything from the leaves to the sellers can capture all that 41.000% profit margin for themselves!
When the biggest markets US and EU "dry up" for illegal sales of cocaine, the gangs literally don't have anyone any more to extort for money - the population of South America is dirt poor. And also, they can't afford running militia that are more capable than some nations' armies or bribing the utter majority of the political class any more once these tasty US dollars vanish.
>“It is difficult to get a man to understand something, when his salary depends on his not understanding it.”
Upton Sinclair ~ 1934
https://www.goodreads.com/quotes/21810-it-is-difficult-to-ge...
Searching for their profile on their employers website, and you'll find not a single criminal case. As was to be expected, considering the vast majority of lawsuits are civil law matters.