So wait, were the cartels sitting around ignoring heroin/coke/meth as long as marijuana was illegal? That makes no sense.

Not every cartel will go out of business immediately, but if you cut off a big source of illegal funds it absolutely will mean less illegal activity.

They weren't, but like all big corporations, they diversified their product lines:

- Losing marijuana business, Mexican cartels push heroin and meth -https://www.washingtonpost.com/world/the_americas/losing-mar...

- Marijuana Legalization Sparks Heroin, Meth Trade Increase with Mexican Cartels - https://www.thefix.com/content/marijuana-legalization-sparks...

- Drug Cartels Turning to Meth, Heroin After Pot Legalization in U.S. - http://insider.foxnews.com/2015/05/19/drug-cartels-turning-m...

- Have Changing Marijuana Laws Led to an Increase in Heroin & Meth Smuggling? - http://lighthouserecoveryinstitute.com/have-changing-marijua...

Also, marijuana was never much money for the cartels, the real money has always been in heroin and meth. It's much cheaper to produce and the profit margins are much better than weed.

If you want to cut off their biggest sources of illegal activity, you're not only going to have to legalize some pretty serious drugs, you're also going to have to legalize kidnapping, murder, blackmail and racketeering. The idea that the only way cartels make money is on drugs is terribly myopic.

I'm not saying we should legalise all profitable things. But when the profit:social harm ratio is large, making them illegal may do more harm than good. Every extra product line helps the cartels - if it wasn't profitable they wouldn't be doing it. Kidnapping and racketeering are expensive and dangerous; drugs are not their only source of income but they are a big one.

It's the same logical leap as legalizing alcohol during the prohibition era reduced violence [1]. See Figure 4 - Homicide Rate (1910 - 1944).

[1]: http://www.cato.org/pubs/pas/pa-157.html

The idea is to legalize and control all drugs. Where will the cartels get their money from?

Some drugs are still going to be cheaper from the illegal market. Criminal gangs don't pay tax; sometimes use slave labour; don't have the best quality control; etc.

See also the amount of counterfeit and smuggled cigarettes in the UK.

True but the effect is likely to be fairly small. It's probably better to compare legalization of most drugs to the end of prohibition. That saw a collapse in crime and incarceration rates back towards (although admittedly not all the way down to) pre-prohibition levels which only picked up again with the war on drugs.

If you don't trust that comparison, how about looking at the actual real world effects seen recently in Western countries such as Holland and Portugal that have tried this.

Yes, but it's still a problem.

UK customs agents seize about 1m cigarettes per day. There are about 10m smokers in the UK, so if they smoke about 20 a day that's about 200m cigarettes per day. 1m isn't much compared to that. But it's still there.

(But I do strongly support legalisation of drugs. I just think there's some stuff to be learnt from UK)

The black market is a natural limit on the "effectiveness" of sales taxes. High enough taxes constitute de facto prohibition, especially for poorer segments of the market. Thus a high enough tax can't really be justified by the goals of collecting funds or discouraging vice. The criminal activity is the point; how else could they justify employing so many more police than a rational system of laws would require?