Capitol Hill's drug warriors self-injected their latest fix of high dudgeon in early March, after the abduction of four Americans — two of whom were subsequently murdered — by drug traffickers in Mexico. On March 8, US senators Roger Marshall, from Kansas, and Rick Scott, from Florida, announced proposed legislation to designate Mexican drug cartels as “terrorist organisations”.

Marshall admitted more than he probably intended on the subject when he described the abductions/murders as “a tragedy and a symptom of a larger problem stemming from the culture supported by our national leadership”.

Why do Mexican drug cartels exist? Why do they smuggle cocaine, heroin and other substances into the United States? Why are they willing to kill to protect their turf and snuff out competition?

Because, as Willie Sutton supposedly said when asked why he robbed banks, “that’s where the money is”.

Why is that where the money is?

Because politicians such as Roger Marshall and Rick Scott want it there, that’s why.

After a century of the “war on drugs”, a few lessons that were obvious from its beginning remain glaringly so.

Lesson 1: some people like to use drugs, and are going to do so whether or not they have Marshall’s and Scott’s permission to do so.

Lesson 2: most people like to make money, and some are going to do so by providing drug users with drugs, whether or not they have Marshall’s and Scott’s permission to do so.

Lesson 3: the kind of people who are willing to make money without the permission of Marshall and Scott are also willing to kill to keep making that money.

Lesson 4: there is nothing Marshall and Scott can do to change Lessons 1, 2 and 3.

Those lessons explain why we don’t very often see aspirin or beer distributors gunning down their rivals on the street.

When customers can walk into a variety of stores to buy what they want — in known quantity, quality and strength — and when trade disputes can be settled with lawyers rather than with guns, everyone is a lot safer.

Marshall and Scott don’t want you to be safer. They want you, and those who sell you the things you want, to live in terror of their disapproval. They are, in a word, terrorists.

Oddly enough, they are also both veteran drug dealers themselves — Marshall as a prescription-writing obstetrician, and Scott as a “healthcare executive” who parlayed a fortune made facilitating Medicare fraud into a career in politics.

The continuing terror campaigns they order and sanction — from abducting merchants and customers off the street and putting them in cages, to deploying police and troops abroad to violently suppress dealers — guarantee that their opponents will likewise turn to terror.

Marshall, Scott and the cartels are mutually supporting peas in a rotten pod.

• Thomas L. Knapp is director and senior news analyst at the William Lloyd Garrison Centre for Libertarian Advocacy Journalism