Conspiracy theories in the United States are as common as mass murderers. Nor are they the monopoly of any one ideology. Today, crackpots on the right have no doubt that Barack Obama is a Kenyan-born Muslim who orchestrated the massacre at Newtown's Sandy Hook public school as a ruse to confiscate all guns from freedom-loving Americans while he raises a private black army to slaughter whites. You know I couldn't make this up.

On the left, meanwhile, it's widely believed that the 1 per cent plot behind closed doors to enhance their own influence and wealth while battling unions, environmental groups, social programs, dissent and any laws that regulate their behavior, regardless of the harm this causes the 99 per cent. So yes, many lefties are indeed paranoid. But that doesn't mean they're wrong.

On the contrary. Mountains of evidence exist to prove they're right. Here are four examples.

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In 1971, in a memo called "Attack on the free enterprise system," former Richard Nixon cabinet minister Lewis Powell bemoaned the supposed dominance of liberalism in America and offered a blueprint for conservatives to fight back. Powell shrewdly saw how conservatives could influence every aspect of American life by "financing think tanks, reshaping mass media and seeking influence in universities and the judiciary", which is precisely what happened.

With the generous support of some of America's richest men, this initiative transformed America. Even when moderate liberals like Clinton and Obama have dominated politically, the goalposts have moved so dramatically to the right that they govern as middle-of-the-road Republicans once did, while moderate Republicans are as dead as the dodo.

Or consider one of the great criminal conspiracies of the 20th century, eventually exposed in all its sordid details. In December 1953, America's six largest tobacco companies met at New York's Plaza Hotel to deal with emerging scientific studies documenting nicotine's addictiveness and the ghastly health hazards of smoking. This began their long co-ordinated campaign of lies, deceit, denial and cover-ups in which the health of the tobacco giants trumped any concern for the health of smokers.

According to William Farone, Philip Morris' director of applied research from 1976 to 1984, the tobacco companies created the Tobacco Institute "to simultaneously deny or distort legitimate science." At the same time, the companies deliberately schemed to lure young people into smoking.

This profit-driven conspiracy lasted for half a century until governments in both the U.S. and Canada, pressed by anti-smoking advocates, finally began suing the tobacco companies; cases continue to this day. Whereupon Big Tobacco promptly turned the full irresistible force of its marketing geniuses on the multitudes in the world's poorer countries. The incidence of lung cancer and other tobacco-related disease is already increasing in these areas and will soar even more, another triumph for the free market and its beneficiaries.

American capitalism learns quickly. Combining the Lewis Powell and Big Tobacco strategies, the giant American fossil fuel industry similarly pumps out reams of dubious information to discredit global warming. We learned that multibillionaires like the Koch brothers have quietly been funding such efforts, as I reported in this space last year. But only this month the Guardian revealed that yet another group of anonymous 1-per-cent-ers have delivered another $120-million between 2002 and 2010 to more than 100 groups dedicated to denying climate change. Sanity, science and Suzuki barely have a chance.

Now we learn that yet another vast conspiracy endangers every one of us every time we put a morsel of food in our mouths. In a dramatic new book by journalist Michael Moss, Salt Sugar Fat: How the Food Giants Hooked Us, much reported on by Canadian media this week, we learn that the gargantuan processed food industry – everyone from Coca Cola to Nabisco, General Mills and Kraft – deliberately uses salt, sugar and fat to addict us to foods that are terrible for our health. In the terrifying words of one review, Moss "infiltrates the most disastrous cartel of modern times: a processed food industry that's making a fortune by slowly poisoning an unwitting population."

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The book is " jammed with startling disclosures [and] jaw-dropping confessions." Moss somehow got executives of the world's largest food companies to admit what left-wingers have always said: their only job is to maximize sales and profits in whatever ways necessary. So using top-notch scientists to meticulously ensure their products are irresistible to normal folk, they deliberately add precise quantities of – yes, you got it – salt, sugar, and fat to everyday foods which we addicted consumers can simply not stop devouring in hazardous amounts.

At the same time, not surprisingly, many of these same corporations earnestly pledge, as the Globe reported just this week, not to aim their junk-food commercials at children, just us grown-ups. This, I take it, is what's known as corporate social responsibility.

While health problems multiply and the economic consequences of our atrocious diets go through the roof, the titans of the processing food industry thrive. They're obviously as addicted to their treasure as we are to their irresistible products. So maybe there is no sinister conspiracy. After all, capitalists must do what capitalists must do. It's in their nature.