These are not the best of times to be a political cartoonist. Last week, one of Canada’s top cartoonists, Michael de Adder, had his contract terminated by a publishing company in New Brunswick after a cartoon he did on US President Donald Trump went viral on social media.

The cartoon featured the image of a father and daughter who drowned in the Rio Grande River while attempting to cross into the United States, lying face down in water surrounded by reeds and interrupting the president’s game of golf. “Do you mind if I play through?” asks Trump.

Although there is a dispute over whether the cartoon was the reason for de Adder being let go – Brunswick News Inc says it wasn’t and that negotiations to replace him had been ongoing for some time – it is undeniable that the incident comes at a time when political cartoonists around the world seem to be on the chopping block.

Just weeks before de Adder was let go, the New York Times decided to stop publication of political cartoons after it was severely criticised on social media for publication of a cartoon that was deemed anti-Semitic – although, again, the Times says that its decision had been in the works for some time.

In Kenya too, world-famous cartoonist Godfrey Mwampembwa, also known as GADO, was fired from the Daily Nation in 2015 partly as a result of government pressure.

In Turkey, Musa Kart, cartoonist for the country’s oldest newspaper is in jail. Malaysian cartoonist Zunar has had his books banned and has faced multiple charges of sedition. In Venezuela, Nicaragua and Russia, cartoonists have been forced into exile, while in the US, some have been fired for being too critical of Trump.

According to Terry Anderson, Deputy Executive Director of Cartoonists Rights Network International, which monitors threats and abuses against cartoonists, since 1999 over a hundred cartoonists have been victims of “murder, assault, kidnapping, physical intimidation, imprisonment, arrest, travel bans, police harassment, politically motivated lawsuits, freezing or seizure of assets, vandalism, cyber attack, online harassment, blacklisting and bullying”.

In their paper, Censorship and the Political Cartoonist, Dr Haydon Manning and Dr Robert Phiddian, both of Flinders University, note that political cartoonists are the “canaries sent down the mine shaft of public debate to discover how fresh the air is there, how safe for freedom of speech”. If that is the case, then the air today is positively toxic for democracy.

Reports from Freedom House, which has been tracking global media freedom for the last 40 years, show that the press has been under sustained attack for the last two decades. Its 2010 report had noted that the 2000s had witnessed an effort to restrict media freedom and that the internet and other new media “had become sites of contestation between citizens attempting to provide and access news and governments attempting to maintain control”.

Its latest report observes that in the following decade, global media freedoms have continued to deteriorate, “with new forms of repression taking hold in open societies and authoritarian states alike”.

While much of the blame for this is laid at the feet of politicians and governments, corporations and the internet are as much to blame. The concentration of media ownership in the hands of a few firms has diminished the space for critical journalism.

In New Brunswick, for example, the Irving family, one of the wealthiest in Canada and owners of Brunswick News Inc, has had a de facto monopoly on the media in the province for decades, operating virtually all of the major print publications. This not only means that now de Adder is unable to get any of his cartoons published in his home province, but that coverage of issues tends to be informed by the Irvings’ corporate interests.

In Kenya, according to a report released last year by the Omidyar Network, “every one of the establishment media houses is owned by either a politician, a close party affiliate, or a business person with commercial interests that depend on politicians’ good graces”.

Media coverage tends to be limited, if not directly dictated, by political and corporate interests. The sequence of events that led to GADO’s exit from the Nation Media Group, the owner of the Daily Nation, was sparked by the banning in Tanzania of The East African, a regional weekly owned by the group, following the publication of his cartoon caricaturing then Tanzanian President Jakaya Kikwete.

Further, as newspaper revenues from advertising continue to plummet, this has given big advertisers, “huge influence, which often allows them to quietly control what is published and what is not,” according to the Committee to Protect Journalists. This “back-door soft censorship, generally invisible to the public,” is a filter through which not just cartoonists’ images, but also news reports, must pass before they are published.

However, it is not just advertisers that the media fears. Social media has also emerged as a critical threat. While platforms such as Twitter can provide valuable avenues for constructive audience feedback, they can also be a means of censorship. “We are in a world where moralistic mobs gather on social media and rise like a storm, falling upon newsrooms in an overwhelming blow,” wrote Patrick Chappate on his blog following the New York Times decision to stop publishing his cartoons.

“This requires immediate counter-measures by publishers, leaving no room for ponderation or meaningful discussions. Twitter is a place for furor, not debate. The most outraged voices tend to define the conversation, and the angry crowd follows in.”

The need to avoid provoking the online outrage machine, which can lead to loss of subscriptions and ad revenues, makes media less willing to publish articles, images and cartoons that do not conform to popular opinion.

Today, under the banner of outrage, fortifications are being erected around topics – from religion to race – deemed “sensitive”, placing them out of the reach of public comment or satire. That can be fatal to democracy which depends on a free contestation of ideas, even those that offend.

As the late US Supreme Court Justice Oliver Wendell Holmes Jr said, “If there is any principle… that more imperatively calls for attachment than any other it is the principle of free thought – not free thought for those who agree with us but freedom for the thought that we hate.”

The death of the political cartoon, whether at the hand of the state, in pursuit of profit or as a sacrifice to appease online mobs, is a warning sign and a herald of the diminution of political freedoms. The canaries are dying. But is anyone paying attention?

The views expressed in this article are the author’s own and do not necessarily reflect Al Jazeera’s editorial stance.